diff --git a/src/Client.php b/src/Client.php
index ca435f4..d8829d3 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -292,7 +292,8 @@ private function request($method, $endpoint, array $query=array(), array $payloa
         curl_setopt($ch, CURLOPT_CUSTOMREQUEST, $method);
         
         if ($method == 'POST') {
-            curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
+            $data = $img_svc_url ? $payload : json_encode($payload);
+            curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
         }
         
         $result = curl_exec($ch);