Hi,
I'm developing in C# but that's not the point. The HTTP request is the problem. I really don't know what is going on... On the screenshot you can see my request and the response: http://gyazo.com/cfb7e35958f8c4ec8be8f668ecf0737e
The ordernumber is 100% correct. I checked it and the response for a not existing Ordernumber is different (404 not found instead of 400)
The authentication is working. When I send request via GET, I get an empty JSON object.