diff --git a/src/Http/Client.php b/src/Http/Client.php
index afdd310..eb31d52 100644
--- a/src/Http/Client.php
+++ b/src/Http/Client.php
@@ -17,7 +17,10 @@ public function __construct($apiKey)
 
         parent::__construct([
             'base_uri' => 'https://api.shipcloud.io/v1/',
-            'auth' => [$apiKey, null]
+            'auth' => [$apiKey, null],
+            'headers' => [
+                'Content-Type' => 'application/json'
+            ]
         ]);
     }