Http 404 error while consuming RESTful service in .Net passing data in JSON format

Getting HTTP 404 Error while Consuming RESTful service in .Net passing data in JSON format"

getting HTTP 404 in response at line  also in bold
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 HttpWebResponse response = (HttpWebResponse)request.GetResponse();        
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string json = "{"
                                          + "\"username\" : \"username@email.com\","
                                          + "\"password\" : \"password1@\""
                                          + "}";
                  
                  const string serviceURL = "https://api.wheniwork.com/login";

                  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(serviceURL);
                  
                  request.ContentType = "application/json; charset=utf-8"; //set the content type to JSON
            request.Method = "POST"; //make an HTTP POST
                  //request.Headers.Add("Authorization", "W-Key=key");
                  request.Headers.Add("W-Key", "key");

                  using (var streamWriter = new StreamWriter(request.GetRequestStream()))
                  {
                        //initiate the request
                        JavaScriptSerializer serializer = new JavaScriptSerializer();
                        var resToWrite = serializer.Deserialize<Dictionary<string, object>>(json);
                        streamWriter.Write(resToWrite);
                        streamWriter.Flush();
                        streamWriter.Close();
                  }

                  Stream requestStream = request.GetRequestStream();

                  requestStream.Write(Encoding.ASCII.GetBytes(json), 0, json.Length);
                  requestStream.Close();

            // Get the response.
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();              
            var streamReader = new StreamReader(response.GetResponseStream());                
            var result = streamReader.ReadToEnd();