400 Bad request with casablanca cpprestsdk

http_request request(methods::POST); request.headers().add(L"Content-Type", L"application/json; charset=utf-8"); request.headers().add(L"X-Requested-With", L"XMLHttpRequest"); request.set_body(body);

The code above gives the following output:

HTTP/1.1 400 Bad Request Connection: close Content-Length: 334 Content-Type: text/html; charset=us-ascii Date: Fri, 10 Mar 2017 23:05:43 GMT Server: Microsoft-HTTPAPI/2.0

Can you tell me what's wrong with my parameters?