Redmine

I try to update the relations via Json. But I don´t get the format right. I´m using C#. I got 402 Exception, wrong Format.

Thanks for any help.

Here my Code:

var httpWebRequest = (HttpWebRequest)WebRequest.Create("http://" + Constants.REDMINE_HOST + "/" + Constants.REDMINE_SERVER + "/" + "issues/" + id + "/relations" + ".json" + "?key=Constants.mykey");
            httpWebRequest.ContentType = "text/json";
            httpWebRequest.Method = "POST";
            httpWebRequest.Accept = "application/json";

            using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
            {
                string json = "{relation: {\"issue_to_id\" : 499 \"relation_type\" : \"relates\"}}";

                streamWriter.Write(json);
                streamWriter.Flush();
                streamWriter.Close();

                try
                { 
                var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    var result = streamReader.ReadToEnd();
                }
            }

            catch(Exception e)
            {
                Console.WriteLine(e);
            }