getUrl got "internal exception" return.

getUrl got "internal exception" return.

The following code 
  2.     url = "https://xxxxx.weclapp.com/webapp/api/v1";
  3.     header = map();
  4.     header.put("AuthenticationToken", "xxxxxxxx-xxxx-xxx-xxx-xxxxxxxxxxxxx");
  5.     response = getUrl(url, header,false);
  6.     info response;
  7.     return;
delivers the following result

{"responseText":"internal exception","responseCode":"-1"}


It does work with postman.

Has anybody a clue what could be the problem and how to do the troubleshooting?

Thanks in advance.