diff --git a/src/class-convertkit-api-v4.php b/src/class-convertkit-api-v4.php
index cfde53e..3b72f5b 100644
--- a/src/class-convertkit-api-v4.php
+++ b/src/class-convertkit-api-v4.php
@@ -492,6 +492,7 @@ public function get_access_token_by_api_key_and_secret( $api_key, $api_secret )
 			array(
 				'api_key'    => $api_key,
 				'api_secret' => $api_secret,
+				'client_id'  => $this->client_id,
 			)
 		);
 
diff --git a/tests/wpunit/APITest.php b/tests/wpunit/APITest.php
index f1af417..f1dadf0 100644
--- a/tests/wpunit/APITest.php
+++ b/tests/wpunit/APITest.php
@@ -604,6 +604,38 @@ public function testGetAccessTokenByInvalidAPIKeyAndSecret()
 		$this->assertEquals('Authorization Failed: API Secret not valid', $result->get_error_message());
 	}
 
+	/**
+	 * Test that fetching an Access Token using an invalid client ID returns a WP_Error.
+	 *
+	 * @since   2.0.7
+	 */
+	public function testGetAccessTokenByAPIKeyAndSecretWithInvalidClientID()
+	{
+		$api    = new ConvertKit_API_V4( 'invalidClientID', $_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'] );
+		$result = $api->get_access_token_by_api_key_and_secret(
+			$_ENV['CONVERTKIT_API_KEY'],
+			$_ENV['CONVERTKIT_API_SECRET']
+		);
+		$this->assertInstanceOf(WP_Error::class, $result);
+		$this->assertEquals($result->get_error_code(), $this->errorCode);
+	}
+
+	/**
+	 * Test that fetching an Access Token using a blank client ID returns a WP_Error.
+	 *
+	 * @since   2.0.7
+	 */
+	public function testGetAccessTokenByAPIKeyAndSecretWithBlankClientID()
+	{
+		$api    = new ConvertKit_API_V4( '', $_ENV['CONVERTKIT_OAUTH_REDIRECT_URI'] );
+		$result = $api->get_access_token_by_api_key_and_secret(
+			$_ENV['CONVERTKIT_API_KEY'],
+			$_ENV['CONVERTKIT_API_SECRET']
+		);
+		$this->assertInstanceOf(WP_Error::class, $result);
+		$this->assertEquals($result->get_error_code(), $this->errorCode);
+	}
+
 	/**
 	 * Test that supplying valid API credentials to the API class returns the expected account information.
 	 *