title: AFNetworking Serialization Response Error
body: <p>I'm using AFNetworking version 3.0 for handling a POST request.
  When I run the code I get an error that says:enter code here</p>
  
  <pre><code>2016-01-26 16:48:50.181 Voluntree[3590:1749083] In order to validate a domain name for self signed certificates, you MUST use pinning.
  2016-01-26 16:48:50.905 Voluntree[3590:1748745] Error: Error Domain=com.alamofire.error.serialization.response Code=-1016 "Request failed: unacceptable content-type: text/plain" UserInfo={com.alamofire.serialization.response.error.response=&lt;NSHTTPURLResponse: 0x13deb83d0&gt; { URL: https://voluntree.imrapid.io/signup_by_email } { status code: 200, headers {
      "Access-Control-Allow-Headers" = "Origin, X-Requested-With, Content-Type, Accept";
      "Access-Control-Allow-Methods" = "POST, GET, OPTIONS, PUT, DELETE, HEAD";
      "Access-Control-Allow-Origin" = "*";
      Connection = "keep-alive";
      "Content-Length" = 4;
      "Content-Type" = "text/plain";
      Date = "Tue, 26 Jan 2016 14:48:50 GMT";
      Server = Cowboy;
      Via = "1.1 vegur";
      "X-Powered-By" = Express;
  } }, NSErrorFailingURLKey=https://voluntree.imrapid.io/signup_by_email, com.alamofire.serialization.response.error.data=&lt;32343634&gt;, NSLocalizedDescription=Request failed: unacceptable content-type: text/plain}
  </code></pre>