diff --git a/src/Mailgun/Api/HttpApi.php b/src/Mailgun/Api/HttpApi.php
index 467689c..e7fcb39 100644
--- a/src/Mailgun/Api/HttpApi.php
+++ b/src/Mailgun/Api/HttpApi.php
@@ -139,7 +139,9 @@ abstract class HttpApi
      */
     protected function httpPost($path, array $parameters = [], array $requestHeaders = [])
     {
-        return $this->httpPostRaw($path, $this->createJsonBody($parameters), $requestHeaders);
+        $requestHeaders['Content-Type'] = 'application/x-www-form-urlencoded';
+
+        return $this->httpPostRaw($path, $this->createRequestBody($parameters), $requestHeaders);
     }
 
     /**
@@ -175,9 +177,11 @@ abstract class HttpApi
      */
     protected function httpPut($path, array $parameters = [], array $requestHeaders = [])
     {
+        $requestHeaders['Content-Type'] = 'application/x-www-form-urlencoded';
+
         try {
             $response = $this->httpClient->sendRequest(
-                $this->requestBuilder->create('PUT', $path, $requestHeaders, $this->createJsonBody($parameters))
+                $this->requestBuilder->create('PUT', $path, $requestHeaders, $this->createRequestBody($parameters))
             );
         } catch (HttplugException\NetworkException $e) {
             throw HttpServerException::networkError($e);
@@ -197,9 +201,11 @@ abstract class HttpApi
      */
     protected function httpDelete($path, array $parameters = [], array $requestHeaders = [])
     {
+        $requestHeaders['Content-Type'] = 'application/x-www-form-urlencoded';
+
         try {
             $response = $this->httpClient->sendRequest(
-                $this->requestBuilder->create('DELETE', $path, $requestHeaders, $this->createJsonBody($parameters))
+                $this->requestBuilder->create('DELETE', $path, $requestHeaders, $this->createRequestBody($parameters))
             );
         } catch (HttplugException\NetworkException $e) {
             throw HttpServerException::networkError($e);
@@ -215,8 +221,8 @@ abstract class HttpApi
      *
      * @return null|string
      */
-    protected function createJsonBody(array $parameters)
+    protected function createRequestBody(array $parameters)
     {
-        return (count($parameters) === 0) ? null : json_encode($parameters, empty($parameters) ? JSON_FORCE_OBJECT : 0);
+        return (count($parameters) === 0) ? null : http_build_query($parameters);
     }
 }