Problems when connect API from iOS

I'm developing some APIs for a web service using asp.net API 2.0. I've deployed a server and tested these APIs in Postman. It works well. However when my iOS team connect APIs, they receive this error:

"handleErrorNetwork: Error Domain=/nameApi/abc Code=-1011 "Request failed: internal server error (500)" UserInfo={com.alamofire.serialization.response.error.response=<NSHTTPURLResponse: 0x7fc5779f1b00> { URL: http://myAPIlink } { status code: 500, headers {
    "Cache-Control" = "no-cache";
    "Content-Length" = 56;
    "Content-Type" = "application/json; charset=utf-8";
    Date = "Tue, 17 Nov 2015 09:38:26 GMT";
    Expires = "-1";
    Pragma = "no-cache";
    Server = "Microsoft-IIS/7.5";
    "X-AspNet-Version" = "4.0.30319";
    "X-Powered-By" = "ASP.NET"; } }, NSErrorFailingURLKey=http://myAPIlink, com.alamofire.serialization.response.error.data=<7b227374 61747573 223a322c 226d6573 73616765 223a2254 68652067 6976656e 20686561 64657220 77617320 6e6f7420 666f756e 642e227d>, NSLocalizedDescription=Request failed: internal server error (500)}

Does anyone known if this problem is client or server issue and how to fix it?

Solution

Error 500 means Internal Server Error. There is something wrong on the server side. To troubleshoot the cause have to look into the logs on the server side.