diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 289ce7d7..bc2f4b86 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -17,6 +17,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          filter: tree:0
       - name: Setup .NET 9.0
         uses: actions/setup-dotnet@v2
         with:
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index 9cce2025..b07ecd53 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -23,6 +23,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          filter: tree:0
       - name: Setup .NET 9.0
         uses: actions/setup-dotnet@v2
         with:
diff --git a/src/TrueLayer/Mandates/IMandatesApi.cs b/src/TrueLayer/Mandates/IMandatesApi.cs
index 41d0c65a..4e8e1ab3 100644
--- a/src/TrueLayer/Mandates/IMandatesApi.cs
+++ b/src/TrueLayer/Mandates/IMandatesApi.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Threading;
 using System.Threading.Tasks;
 using OneOf;
@@ -28,11 +29,15 @@ public interface IMandatesApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
+        /// </param>
+        /// <param name="cancellationToken">The cancellation token to cancel the operation
         /// </param>
-        /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<CreateMandateResponse>> CreateMandate(
-            CreateMandateRequest mandateRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreateMandateRequest mandateRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets a mandate
@@ -42,7 +47,24 @@ Task<ApiResponse<CreateMandateResponse>> CreateMandate(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<MandateDetailUnion>> GetMandate(
-            string mandateId, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
+
+        /// <summary>
+        /// Generates a link to the TrueLayer hosted payment page
+        /// </summary>
+        /// <param name="mandateId">The mandate identifier</param>
+        /// <param name="resourceToken">The resource token, returned from <see cref="CreateMandate"/></param>
+        /// <param name="returnUri">
+        /// Your return URI to which the end user will be redirected after the mandate is completed.
+        /// Note this should be configured in the TrueLayer console under your application settings.
+        /// </param>
+        /// <returns>The HPP link you can redirect the end user to</returns>
+        string CreateHostedPaymentPageLink(
+            string mandateId,
+            string resourceToken,
+            Uri returnUri);
 
         /// <summary>
         /// Lists mandates for a user
@@ -52,7 +74,9 @@ Task<ApiResponse<MandateDetailUnion>> GetMandate(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
-            ListMandatesQuery query, MandateType mandateType, CancellationToken cancellationToken = default);
+            ListMandatesQuery query,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Start the authorization flow for a mandate.
@@ -63,11 +87,16 @@ Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
-            string mandateId, StartAuthorizationFlowRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            StartAuthorizationFlowRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Submit the provider details selected by the PSU.
@@ -78,11 +107,16 @@ Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
-            string mandateId, SubmitProviderSelectionRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            SubmitProviderSelectionRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Submit the consent given by the user
@@ -95,7 +129,11 @@ Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the authorization flow action details if successful, otherwise problem details</returns>
-        Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+        Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Get Confirmation Of Funds
@@ -107,7 +145,11 @@ Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
-            string mandateId, int amountInMinor, string currency, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            int amountInMinor,
+            string currency,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets a mandates constraints
@@ -117,18 +159,26 @@ Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(
-            string mandateId, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Revoke mandate
         /// </summary>
         /// <param name="mandateId">The id of the mandate</param>
+        /// <param name="mandateType">The type of the mandate. Either sweeping or commercial</param>
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payment details if successful, otherwise problem details</returns>
-        Task<ApiResponse> RevokeMandate(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+        Task<ApiResponse> RevokeMandate(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Mandates/MandatesApi.cs b/src/TrueLayer/Mandates/MandatesApi.cs
index 505fe239..b79524be 100644
--- a/src/TrueLayer/Mandates/MandatesApi.cs
+++ b/src/TrueLayer/Mandates/MandatesApi.cs
@@ -6,6 +6,7 @@
 using TrueLayer.Extensions;
 using TrueLayer.Mandates.Model;
 using TrueLayer.Models;
+using TrueLayer.Payments;
 
 namespace TrueLayer.Mandates
 {
@@ -25,12 +26,14 @@ internal class MandatesApi : IMandatesApi
         private readonly TrueLayerOptions _options;
         private readonly Uri _baseUri;
         private readonly IAuthApi _auth;
+        private readonly HppLinkBuilder _hppLinkBuilder;
 
         public MandatesApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options)
         {
             _apiClient = apiClient.NotNull(nameof(apiClient));
             _options = options.NotNull(nameof(options));
             _auth = auth.NotNull(nameof(auth));
+            _hppLinkBuilder = new HppLinkBuilder(options.Payments?.HppUri, options.UseSandbox ?? true);
 
             options.Payments.NotNull(nameof(options.Payments))!.Validate();
 
@@ -39,10 +42,13 @@ public MandatesApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandateRequest mandateRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(
+            CreateMandateRequest mandateRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             mandateRequest.NotNull(nameof(mandateRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var mandateType = mandateRequest.Mandate.Match(
                 vrpCommercial => vrpCommercial.Type,
                 vrpSweeping => vrpSweeping.Type);
@@ -56,7 +62,7 @@ public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandat
             return await _apiClient.PostAsync<CreateMandateResponse>(
                 _baseUri,
                 mandateRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -65,7 +71,10 @@ public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandat
 
         //TODO: is it correct that this method expects a mandate type?
         /// <inheritdoc />
-        public async Task<ApiResponse<MandateDetailUnion>> GetMandate(string mandateId, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<MandateDetailUnion>> GetMandate(
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -85,7 +94,14 @@ public async Task<ApiResponse<MandateDetailUnion>> GetMandate(string mandateId,
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(ListMandatesQuery query, MandateType mandateType, CancellationToken cancellationToken = default)
+        public string CreateHostedPaymentPageLink(string mandateId, string resourceToken, Uri returnUri)
+            => _hppLinkBuilder.Build(mandateId, resourceToken, returnUri);
+
+        /// <inheritdoc />
+        public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
+            ListMandatesQuery query,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
@@ -108,12 +124,17 @@ public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListManda
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(string mandateId, StartAuthorizationFlowRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
+            string mandateId,
+            StartAuthorizationFlowRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
             request.NotNull(nameof(request));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -124,7 +145,7 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.AuthorizationFlow),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -132,12 +153,17 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(string mandateId, SubmitProviderSelectionRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
+            string mandateId,
+            SubmitProviderSelectionRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
             request.NotNull(nameof(request));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -148,18 +174,22 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelecti
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.ProviderSelection),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -170,7 +200,7 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.Consent),
                 null,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -178,7 +208,12 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(string mandateId, int amountInMinor, string currency, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
+            string mandateId,
+            int amountInMinor,
+            string currency,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -198,7 +233,10 @@ public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOf
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(string mandateId, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -218,7 +256,11 @@ public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(str
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse> RevokeMandate(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse> RevokeMandate(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -233,7 +275,7 @@ public async Task<ApiResponse> RevokeMandate(string mandateId, string idempotenc
             return await _apiClient.PostAsync(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.Revoke),
                 null,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
diff --git a/src/TrueLayer/Payments/IPaymentsApi.cs b/src/TrueLayer/Payments/IPaymentsApi.cs
index a8ff9a59..e2acba80 100644
--- a/src/TrueLayer/Payments/IPaymentsApi.cs
+++ b/src/TrueLayer/Payments/IPaymentsApi.cs
@@ -42,11 +42,14 @@ public interface IPaymentsApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created payment if successful, otherwise problem details</returns>
         Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
-            CreatePaymentRequest paymentRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreatePaymentRequest paymentRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets the details of an existing payment
@@ -54,7 +57,9 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// <param name="id">The payment identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payment details if successful, otherwise problem details</returns>
-        Task<ApiResponse<GetPaymentUnion>> GetPayment(string id, CancellationToken cancellationToken = default);
+        Task<ApiResponse<GetPaymentUnion>> GetPayment(
+            string id,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Generates a link to the TrueLayer hosted payment page
@@ -66,7 +71,10 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// Note this should be configured in the TrueLayer console under your application settings.
         /// </param>
         /// <returns>The HPP link you can redirect the end user to</returns>
-        string CreateHostedPaymentPageLink(string paymentId, string paymentToken, Uri returnUri);
+        string CreateHostedPaymentPageLink(
+            string paymentId,
+            string paymentToken,
+            Uri returnUri);
 
         /// <summary>
         /// Start the authorization flow for a payment.
@@ -75,13 +83,14 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="request">The start authorization request details</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns></returns>
         Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
             string paymentId,
-            string idempotencyKey,
+            string? idempotencyKey,
             StartAuthorizationFlowRequest request,
             CancellationToken cancellationToken = default);
 
@@ -92,12 +101,14 @@ Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="request">The create payment refund request</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The id of the created refund</returns>
-        Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymentId,
-            string idempotencyKey,
+        Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
+            string paymentId,
+            string? idempotencyKey,
             CreatePaymentRefundRequest request,
             CancellationToken cancellationToken = default);
 
@@ -107,7 +118,8 @@ Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymen
         /// <param name="paymentId">The payment identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The list of refunds for a payment.</returns>
-        Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(string paymentId,
+        Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(
+            string paymentId,
             CancellationToken cancellationToken = default);
 
         /// <summary>
@@ -117,7 +129,8 @@ Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(string paymentI
         /// <param name="refundId">The refund identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The details of the selected refund</returns>
-        Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
+        Task<ApiResponse<RefundUnion>> GetPaymentRefund(
+            string paymentId,
             string refundId,
             CancellationToken cancellationToken = default);
 
@@ -128,9 +141,13 @@ Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>HTTP 202 Accepted if successful, otherwise problem details.</returns>
-        Task<ApiResponse> CancelPayment(string paymentId, string idempotencyKey, CancellationToken cancellationToken = default);
+        Task<ApiResponse> CancelPayment(
+            string paymentId,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs b/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
index b6140063..d3a84cab 100644
--- a/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
+++ b/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
@@ -2,6 +2,7 @@
 
 namespace TrueLayer.Payments.Model;
 
-public record CreatePaymentRefundRequest(string Reference,
+public record CreatePaymentRefundRequest(
+    string Reference,
     uint? AmountInMinor = null,
     Dictionary<string, string>? Metadata = null);
diff --git a/src/TrueLayer/Payments/PaymentsApi.cs b/src/TrueLayer/Payments/PaymentsApi.cs
index f53e0d85..9178f107 100644
--- a/src/TrueLayer/Payments/PaymentsApi.cs
+++ b/src/TrueLayer/Payments/PaymentsApi.cs
@@ -55,10 +55,9 @@ public PaymentsApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRequest paymentRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRequest paymentRequest, string? idempotencyKey = null, CancellationToken cancellationToken = default)
         {
             paymentRequest.NotNull(nameof(paymentRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest(AuthorizationScope.Payments), cancellationToken);
 
@@ -70,7 +69,7 @@ public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRe
             return await _apiClient.PostAsync<CreatePaymentUnion>(
                 _baseUri,
                 paymentRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -105,13 +104,15 @@ public string CreateHostedPaymentPageLink(string paymentId, string paymentToken,
         /// <inheritdoc />
         public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
             string paymentId,
-            string idempotencyKey,
+            string? idempotencyKey,
             StartAuthorizationFlowRequest request,
             CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
+
             paymentId.NotAUrl(nameof(paymentId));
             idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+            
             request.NotNull(nameof(request));
 
             var authResponse = await _auth.GetAuthToken(
@@ -125,15 +126,18 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.AuthorizationFlow),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymentId,
-            string idempotencyKey, CreatePaymentRefundRequest request, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
+            string paymentId,
+            string? idempotencyKey,
+            CreatePaymentRefundRequest request,
+            CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
             paymentId.NotAUrl(nameof(paymentId));
@@ -150,7 +154,7 @@ public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
             return await _apiClient.PostAsync<CreatePaymentRefundResponse>(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.Refunds),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -204,9 +208,13 @@ public async Task<ApiResponse<RefundUnion>> GetPaymentRefund(
             );
         }
 
-        public async Task<ApiResponse> CancelPayment(string paymentId, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse> CancelPayment(
+            string paymentId,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
+
             paymentId.NotAUrl(nameof(paymentId));
             idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
@@ -220,7 +228,7 @@ public async Task<ApiResponse> CancelPayment(string paymentId, string idempotenc
 
             return await _apiClient.PostAsync(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.Cancel),
-                idempotencyKey: idempotencyKey,
+                idempotencyKey: idempotencyKey ?? Guid.NewGuid().ToString(),
                 accessToken: authResponse.Data!.AccessToken,
                 signingKey: _options.Payments!.SigningKey,
                 cancellationToken: cancellationToken);
diff --git a/src/TrueLayer/Payouts/IPayoutsApi.cs b/src/TrueLayer/Payouts/IPayoutsApi.cs
index d1266268..6ecb7021 100644
--- a/src/TrueLayer/Payouts/IPayoutsApi.cs
+++ b/src/TrueLayer/Payouts/IPayoutsApi.cs
@@ -25,11 +25,14 @@ public interface IPayoutsApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created payout if successful, otherwise problem details</returns>
         Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
-            CreatePayoutRequest payoutRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreatePayoutRequest payoutRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets the details of an existing payment
@@ -37,6 +40,8 @@ Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
         /// <param name="id">The payout identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payout details if successful, otherwise problem details</returns>
-        Task<ApiResponse<GetPayoutUnion>> GetPayout(string id, CancellationToken cancellationToken = default);
+        Task<ApiResponse<GetPayoutUnion>> GetPayout(
+            string id,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Payouts/PayoutsApi.cs b/src/TrueLayer/Payouts/PayoutsApi.cs
index 937a7041..a39232a4 100644
--- a/src/TrueLayer/Payouts/PayoutsApi.cs
+++ b/src/TrueLayer/Payouts/PayoutsApi.cs
@@ -37,10 +37,12 @@ public PayoutsApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options)
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(CreatePayoutRequest payoutRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
+            CreatePayoutRequest payoutRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             payoutRequest.NotNull(nameof(payoutRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest(AuthorizationScope.Payments), cancellationToken);
 
@@ -52,14 +54,16 @@ public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(CreatePayoutRe
             return await _apiClient.PostAsync<CreatePayoutResponse>(
                 _baseUri,
                 payoutRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<GetPayoutUnion>> GetPayout(string id, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetPayoutUnion>> GetPayout(
+            string id,
+            CancellationToken cancellationToken = default)
         {
             id.NotNullOrWhiteSpace(nameof(id));
             id.NotAUrl(nameof(id));
diff --git a/test/TrueLayer.AcceptanceTests/MandatesTests.cs b/test/TrueLayer.AcceptanceTests/MandatesTests.cs
index 6448de91..b1cc7448 100644
--- a/test/TrueLayer.AcceptanceTests/MandatesTests.cs
+++ b/test/TrueLayer.AcceptanceTests/MandatesTests.cs
@@ -38,8 +38,7 @@ public async Task Can_Get_Mandate(CreateMandateRequest mandateRequest)
         {
             // Arrange
             var client = _fixture.TlClients[0];
-            var createResponse = await client.Mandates.CreateMandate(
-                mandateRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var createResponse = await client.Mandates.CreateMandate(mandateRequest);
             createResponse.StatusCode.Should().Be(HttpStatusCode.Created);
             var mandateId = createResponse.Data!.Id;
             var mandateType = mandateRequest.Mandate.Match(
@@ -63,8 +62,7 @@ public async Task Can_List_Mandate(CreateMandateRequest mandateRequest)
         {
             // Arrange
             var client = _fixture.TlClients[0];
-            var createResponse = await client.Mandates.CreateMandate(
-                mandateRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var createResponse = await client.Mandates.CreateMandate(mandateRequest);
             createResponse.StatusCode.Should().Be(HttpStatusCode.Created);
 
             // Act
@@ -82,8 +80,7 @@ public async Task Can_Start_Preselected_Authorization(CreateMandateRequest manda
         {
             // Arrange
             var client = _fixture.TlClients[0];
-            var createResponse = await client.Mandates.CreateMandate(
-                mandateRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var createResponse = await client.Mandates.CreateMandate(mandateRequest);
             var mandateId = createResponse.Data!.Id;
             StartAuthorizationFlowRequest authorizationRequest = new(
                 new ProviderSelectionRequest(),
@@ -119,8 +116,7 @@ public async Task Can_Complete_UserSelected_Full_Auth_Flow(CreateMandateRequest
             // Arrange
             var client = _fixture.TlClients[0];
             const string providerId = "mock-payments-gb-redirect";
-            var createResponse = await client.Mandates
-                .CreateMandate(mandateRequest, Guid.NewGuid().ToString());
+            var createResponse = await client.Mandates.CreateMandate(mandateRequest);
 
             var mandateId = createResponse.Data!.Id;
             var mandateType = mandateRequest.Mandate.Match(
@@ -210,9 +206,7 @@ public async Task Can_Create_Mandate_Payment(CreateMandateRequest mandateRequest
             var paymentRequest = RequestBuilders.CreateTestMandatePaymentRequest(mandateRequest, mandateId, false);
 
             // Act
-            var response = await _fixture.TlClients[0].Payments.CreatePayment(
-                paymentRequest,
-                idempotencyKey: Guid.NewGuid().ToString());
+            var response = await _fixture.TlClients[0].Payments.CreatePayment(paymentRequest);
 
             // Assert
             response.StatusCode.Should().Be(HttpStatusCode.Created);
diff --git a/test/TrueLayer.AcceptanceTests/PaymentTests.cs b/test/TrueLayer.AcceptanceTests/PaymentTests.cs
index d1740701..35d23259 100644
--- a/test/TrueLayer.AcceptanceTests/PaymentTests.cs
+++ b/test/TrueLayer.AcceptanceTests/PaymentTests.cs
@@ -54,8 +54,7 @@ public async Task Can_Create_External_Account_Payment(CreatePaymentRequest payme
     {
         foreach (var client in _fixture.TlClients)
         {
-            var response = await client.Payments.CreatePayment(
-                paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var response = await client.Payments.CreatePayment(paymentRequest);
 
             response.StatusCode.Should().Be(HttpStatusCode.Created);
             var authorizationRequired = response.Data.AsT0;
@@ -119,8 +118,7 @@ public async Task Can_Create_Merchant_Account_Gbp_Verification_Payment()
                 Verification = new Verification.Automated { RemitterName = true }
             });
 
-        var response = await _fixture.TlClients[0].Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.TlClients[0].Payments.CreatePayment(paymentRequest);
 
         response.StatusCode.Should().Be(HttpStatusCode.Created);
         var authorizationRequired = response.Data.AsT0;
@@ -150,8 +148,7 @@ public async Task Can_Create_Merchant_Account_Eur_Payment()
             new RelatedProducts(new SignupPlus()),
             new Beneficiary.MerchantAccount(_fixture.ClientMerchantAccounts[0].EurMerchantAccountId));
 
-        var response = await _fixture.TlClients[0].Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.TlClients[0].Payments.CreatePayment(paymentRequest);
 
         response.StatusCode.Should().Be(HttpStatusCode.Created);
         var authorizationRequired = response.Data.AsT0;
@@ -180,8 +177,7 @@ public async Task Can_Create_Payment_With_Auth_Flow()
             providerSelection,
             sortCodeAccountNumber,
             initAuthorizationFlow: true);
-        var response = await _fixture.TlClients[0].Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.TlClients[0].Payments.CreatePayment(paymentRequest);
 
         response.StatusCode.Should().Be(HttpStatusCode.Created);
         response.Data.IsT3.Should().BeTrue();
diff --git a/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj b/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
index b35f951e..663b6093 100644
--- a/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
+++ b/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
@@ -8,8 +8,8 @@
       <WarningsAsErrors>nullable;</WarningsAsErrors>
     </PropertyGroup>
     <ItemGroup>
-      <PackageReference Include="FluentAssertions" Version="6.12.2" />
-      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+      <PackageReference Include="FluentAssertions" Version="7.0.0" />
+      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
       <PackageReference Include="xunit" Version="2.9.2" />
       <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
diff --git a/test/TrueLayer.Tests/TrueLayer.Tests.csproj b/test/TrueLayer.Tests/TrueLayer.Tests.csproj
index 9d8aadde..96a328af 100644
--- a/test/TrueLayer.Tests/TrueLayer.Tests.csproj
+++ b/test/TrueLayer.Tests/TrueLayer.Tests.csproj
@@ -17,7 +17,7 @@
             <PrivateAssets>all</PrivateAssets>
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
         </PackageReference>
-        <PackageReference Include="FluentAssertions" Version="6.12.2"/>
+        <PackageReference Include="FluentAssertions" Version="7.0.0" />
         <PackageReference Include="RichardSzalay.MockHttp" Version="7.0.0" />
         <PackageReference Include="Microsoft.Extensions.Configuration" Version="9.0.0" />
     </ItemGroup>