diff --git a/README.md b/README.md
index 5dc64e5..9d66930 100644
--- a/README.md
+++ b/README.md
@@ -111,7 +111,8 @@ To do this we need to transform our payment request to an API request:
     
 Now we have an API Request that we can execute using our API Connection:
 
-    $apiResponse = $apiConnection->execute($apiRequest);
+    $requestHeaders = []; // Optional request headers
+    $apiResponse = $apiConnection->execute($apiRequest, $requestHeaders);
 
 ### Handling the responses
 
diff --git a/composer.json b/composer.json
index f35e40a..3a28153 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
     "name": "payvision/payvision-sdk-php",
     "description": "Payvision PHP SDK",
     "type": "library",
-    "version": "4.0.0",
+    "version": "4.1.0",
     "license": "MIT",
     "require": {
         "php": "^7.0.13|^7.1",
diff --git a/src/Application/Payments/Service/Marshaller.php b/src/Application/Payments/Service/Marshaller.php
index 7e8ab9d..546c854 100644
--- a/src/Application/Payments/Service/Marshaller.php
+++ b/src/Application/Payments/Service/Marshaller.php
@@ -61,7 +61,7 @@ private function marshall($object, string $targetObject)
             return JsonToObject::build($targetObject, $json);
         } catch (Exception $exception) {
             throw new Exception(
-                \sprintf('Error while marshalling object: %1', $exception->getMessage())
+                \sprintf('Error while marshalling object: %s', $exception->getMessage())
             );
         }
     }
diff --git a/src/Infrastructure/ApiConnection.php b/src/Infrastructure/ApiConnection.php
index 8436d11..f0db4b5 100644
--- a/src/Infrastructure/ApiConnection.php
+++ b/src/Infrastructure/ApiConnection.php
@@ -70,15 +70,16 @@ public function __construct(
 
     /**
      * @param Request $request
+     * @param array $requestHeaders
      * @return mixed
      * @throws ApiException
      * @throws BuilderException
      * @throws ErrorResponse
      */
-    public function execute(Request $request)
+    public function execute(Request $request, array $requestHeaders = [])
     {
         $this->validateResponseClasses($request);
-        $jsonResponse = $this->doRequest($request);
+        $jsonResponse = $this->doRequest($request, $requestHeaders);
         return $this->handleResponse($jsonResponse, $request);
     }
 
@@ -103,14 +104,15 @@ public function executeAndReturnArray(Request $request): array
 
     /**
      * @param Request $request
+     * @param RequestHeaderCollection $requestHeaderCollection
      * @return array
      * @throws ApiException
      */
-    private function get(Request $request): array
+    private function get(Request $request, RequestHeaderCollection $requestHeaderCollection): array
     {
         $guzzleResponse = $this->client->get(
             $request->getUri(),
-            $this->buildRequestArray($request)
+            $this->buildRequestArray($request, $requestHeaderCollection)
         );
 
         $this->lastJsonRequest = $request->getPathParams();
@@ -119,7 +121,7 @@ private function get(Request $request): array
         $json = \json_decode($contents, true);
 
         if (!\is_array($json)) {
-            $this->logDebugData($this->lastJsonRequest, ['_raw_response' => $contents]);
+            $this->logDebugData($this->lastJsonRequest, ['_raw_response' => $contents], $requestHeaderCollection);
             throw new ApiException(
                 \sprintf('Response is not JSON: %1$s', $contents),
                 ApiException::INVALID_RESPONSE
@@ -131,16 +133,17 @@ private function get(Request $request): array
 
     /**
      * @param Request $request
+     * @param RequestHeaderCollection $requestHeaderCollection
      * @return array
      * @throws ApiException
      */
-    private function post(Request $request): array
+    private function post(Request $request, RequestHeaderCollection $requestHeaderCollection): array
     {
         // Build request according to request object
         $jsonRequest = $this->prepareJsonRequest($request);
         $guzzleResponse = $this->client->post(
             $request->getUri(),
-            $this->buildRequestArray($request, $jsonRequest)
+            $this->buildRequestArray($request, $requestHeaderCollection, $jsonRequest)
         );
 
         $this->lastJsonRequest = $jsonRequest;
@@ -149,7 +152,7 @@ private function post(Request $request): array
         $json = \json_decode($contents, true);
 
         if (!\is_array($json)) {
-            $this->logDebugData($this->lastJsonRequest, ['_raw_response' => $contents]);
+            $this->logDebugData($this->lastJsonRequest, ['_raw_response' => $contents], $requestHeaderCollection);
             throw new ApiException(
                 \sprintf('Response is not JSON: %1$s', $contents),
                 ApiException::INVALID_RESPONSE
@@ -162,13 +165,23 @@ private function post(Request $request): array
     /**
      * @param array $jsonRequest
      * @param array $jsonResponse
+     * @param RequestHeaderCollection $requestHeaderCollection
      * @return null
      */
-    private function logDebugData(array $jsonRequest, array $jsonResponse)
-    {
+    private function logDebugData(
+        array $jsonRequest,
+        array $jsonResponse,
+        RequestHeaderCollection $requestHeaderCollection
+    ) {
         $debugData = \sprintf(
-            '%1$sRequest:%1$s%2$s%1$sResponse:%1$s%3$s%1$s',
+            '%1$s%2$sRequest:%1$s%3$s%1$sResponse:%1$s%4$s%1$s',
             \PHP_EOL,
+            \count($requestHeaderCollection) > 0 ?
+                \sprintf(
+                    'Request headers:%1$s%2$s%1$s',
+                    \PHP_EOL,
+                    \json_encode($requestHeaderCollection->getHeaders(), \JSON_PRETTY_PRINT)
+                ) : '',
             \json_encode($jsonRequest, \JSON_PRETTY_PRINT),
             \json_encode($jsonResponse, \JSON_PRETTY_PRINT)
         );
@@ -237,17 +250,19 @@ private function handleResponse(
 
     /**
      * @param Request $request
+     * @param array $requestHeaders
      * @return array
      * @throws ApiException
      */
-    private function doRequest(Request $request): array
+    private function doRequest(Request $request, array $requestHeaders = []): array
     {
+        $requestHeaderCollection = $this->buildRequestHeaderCollection($requestHeaders);
         switch ($request->getMethod()) {
             case Request::METHOD_GET:
-                $jsonResponse = $this->get($request);
+                $jsonResponse = $this->get($request, $requestHeaderCollection);
                 break;
             case Request::METHOD_POST:
-                $jsonResponse = $this->post($request);
+                $jsonResponse = $this->post($request, $requestHeaderCollection);
                 break;
             default:
                 throw new ApiException(
@@ -258,7 +273,7 @@ private function doRequest(Request $request): array
         }
 
         if ($this->debug) {
-            $this->logDebugData($this->lastJsonRequest, $jsonResponse);
+            $this->logDebugData($this->lastJsonRequest, $jsonResponse, $requestHeaderCollection);
         }
 
         return $jsonResponse;
@@ -287,19 +302,40 @@ private function prepareJsonRequest(Request $request): array
 
     /**
      * @param Request $request
+     * @param RequestHeaderCollection $requestHeaderCollection
      * @param array $jsonRequest
      * @return array
      */
-    private function buildRequestArray(Request $request, array $jsonRequest = null): array
-    {
+    private function buildRequestArray(
+        Request $request,
+        RequestHeaderCollection $requestHeaderCollection,
+        array $jsonRequest = null
+    ): array {
         $returnValue = [
             'query' => $request->getPathParams(),
         ];
 
+        if (\count($requestHeaderCollection) > 0) {
+            $returnValue['headers'] = $requestHeaderCollection->getHeaders();
+        }
+
         if ($jsonRequest !== null) {
             $returnValue['json'] = $jsonRequest;
         }
 
         return $returnValue;
     }
+
+    /**
+     * @param string[],array<string> $headers
+     * @return RequestHeaderCollection
+     */
+    private function buildRequestHeaderCollection(array $headers): RequestHeaderCollection
+    {
+        $requestHeader = new RequestHeaderCollection();
+        foreach ($headers as $key => $value) {
+            $requestHeader->add($key, $value);
+        }
+        return $requestHeader;
+    }
 }
diff --git a/src/Infrastructure/RequestHeaderCollection.php b/src/Infrastructure/RequestHeaderCollection.php
new file mode 100644
index 0000000..957d9bf
--- /dev/null
+++ b/src/Infrastructure/RequestHeaderCollection.php
@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Payvision\SDK\Infrastructure;
+
+use ArrayIterator;
+use Countable;
+use IteratorAggregate;
+use Traversable;
+
+class RequestHeaderCollection implements IteratorAggregate, Countable
+{
+    const HEADER_EXECUTION_MODE = 'X-AH-ExecutionMode';
+
+    /**
+     * @var string[],array<string>
+     */
+    protected $headers = [];
+
+    /**
+     * @param string $header
+     * @param string $value
+     * @return $this
+     */
+    public function add(string $header, string $value): self
+    {
+        $this->headers[$header] = $value;
+        return $this;
+    }
+
+    /**
+     * @return ArrayIterator|Traversable
+     */
+    public function getIterator()
+    {
+        return new ArrayIterator($this->headers);
+    }
+
+    /**
+     * @return array
+     */
+    public function getHeaders(): array
+    {
+        return $this->headers;
+    }
+
+    /**
+     * @return int
+     */
+    public function count(): int
+    {
+        return \count($this->headers);
+    }
+}
diff --git a/tests/Test/Unit/Infrastructure/RequestHeaderCollectionTest.php b/tests/Test/Unit/Infrastructure/RequestHeaderCollectionTest.php
new file mode 100644
index 0000000..d9bc31e
--- /dev/null
+++ b/tests/Test/Unit/Infrastructure/RequestHeaderCollectionTest.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright Copyright (c) 2018-2019 Payvision B.V. (https://www.payvision.com/)
+ * @license proprietary
+ */
+
+namespace Payvision\SDK\Test\Unit\Infrastructure;
+
+use Payvision\SDK\Infrastructure\RequestHeaderCollection;
+use PHPUnit\Framework\TestCase;
+
+class RequestHeaderCollectionTest extends TestCase
+{
+    /**
+     * @return null
+     */
+    public function testAddRequestHeaderCollectionSuccessfully()
+    {
+        $requestHeaders = new RequestHeaderCollection();
+        $this->assertEquals(0, $requestHeaders->count());
+
+        $requestHeaders->add(RequestHeaderCollection::HEADER_EXECUTION_MODE, 'test');
+        $this->assertEquals(1, $requestHeaders->count());
+
+        foreach ($requestHeaders as $key => $value) {
+            $this->assertEquals(RequestHeaderCollection::HEADER_EXECUTION_MODE, $key);
+            $this->assertEquals('test', $value);
+        }
+
+        $headers = $requestHeaders->getHeaders();
+        $this->assertArrayHasKey(RequestHeaderCollection::HEADER_EXECUTION_MODE, $headers);
+        $this->assertEquals($headers[RequestHeaderCollection::HEADER_EXECUTION_MODE], 'test');
+    }
+}