Stuck getting refresh token

Stuck getting refresh token

string url = "refresh_token=" + rtoken;
            url += "&client_id=XXX;
            url += "&client_secret=XXX";
            url += "&redirect_uri= https://portal.client360services.com/zoho/auth.aspx";
            url += "&grant_type=refresh_token";

            WebRequest request = (HttpWebRequest)WebRequest.Create(" https://accounts.zoho.com/oauth/v2/token");

            byte[] data = Encoding.ASCII.GetBytes(url);

            request.Method = "POST";
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;

            Stream stream;
            using (stream = request.GetRequestStream())
            {
                stream.Write(data, 0, data.Length);
            }

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            string responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

            No matter what I do the responseString is "{\"error\":\"invalid_code\"}"