diff --git a/src/Client.php b/src/Client.php
index 469fe6a..f6c5012 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -39,16 +39,16 @@ public function build(Recipient $recipient, Notification $notification = null, D
         $isPlayload = false;
 
         if (!is_null($notification)) {
-            $result = array_merge($result, $notification());
+            $result = array_replace_recursive($result, $notification());
             $isPlayload = true;
         }
         if (!is_null($data)) {
-            $result = array_merge($result, $data());
+            $result = array_replace_recursive($result, $data());
             $isPlayload = true;
         }
 
         if (!is_null($config)) {
-            $result = array_merge($result, $config());
+            $result = array_replace_recursive($result, $config());
         }
 
         if (!$isPlayload) {
@@ -61,18 +61,27 @@ public function build(Recipient $recipient, Notification $notification = null, D
     /**
      * Fires built message
      */
-    public function fire() {
-        $options = array(
-            'headers' => array(
-                'Authorization' => 'Bearer ' . $this -> credentials -> getAccessToken()
-            )
-        );
+    public function fire($returnResponseArray = false) {
+        if(!isset($this->header_options)){
+            $this->header_options = array(
+                'headers' => array(
+                    'Authorization' => 'Bearer ' . $this -> credentials -> getAccessToken()
+                )
+            );
+        }
+
+        $options = $this->header_options;
         $body = array(
             self::CONTENT_TYPE => $this -> getPayload(),
             self::HTTP_ERRORS_OPTION => false
         );
-        // Class name conflict occurs, when used as "Client"
-        $client = new GuzzleHttp\Client($options);
+
+        if(!isset($this->guzzle_client)){
+            // Class name conflict occurs, when used as "Client"
+            $this->guzzle_client = new GuzzleHttp\Client($options);
+        }
+
+        $client = $this->guzzle_client;
         $response = $client -> request('POST', $this -> getURL(), $body);
 
         if ($response -> getStatusCode() == 200) {