.net钉钉发送企业消息返回40035不合法的参数

.net 钉钉发送企业消息返回 40035 不合法的参数
post的json字符串:"{\"touser\":\"1001|1002\",\"agentid\":\"5199109\",\"msgtype\":\"text\",\"text\":{\"content\":\"来至钉钉测试\"}}"
{"errcode":40035,"errmsg":"不合法的参数"}
以下两个方法都不行，都返回同样的错误。
但 通过 debug.dingtalk.com可以测试成功，json字符串和上面一样 {"touser":"1001|1002","agentid":"5199109","msgtype":"text","text":{"content":"来至钉钉测试"}}
方法内容：
一：
public static string SendRequest(string url, string body, Encoding encode)
        {
            WebClient wc = new WebClient();
            //Encoding enc = Encoding.UTF8;
            wc.Headers["Content-Type"] = "application/json; charset=utf-8";
            return encode.GetString(wc.UploadData(new Uri(url), "POST", encode.GetBytes(body)));
        }
二：
public string PostWebRequest(string postUrl, string paramData, Encoding dataEncode)
        {
            string ret = string.Empty;
            try
            {
                byte[] byteArray = dataEncode.GetBytes(paramData); //转化
                HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));
                webReq.Method = "POST";
                webReq.ContentType = "application/json; charset=utf-8";

                webReq.ContentLength = byteArray.Length;
                Stream newStream = webReq.GetRequestStream();
                newStream.Write(byteArray, 0, byteArray.Length);//写入参数
                newStream.Close();
                HttpWebResponse response = (HttpWebResponse)webReq.GetResponse();
                StreamReader sr = new StreamReader(response.GetResponseStream(), dataEncode);
                ret = sr.ReadToEnd();
                sr.Close();
                response.Close();
                newStream.Close();
            }
            catch (Exception ex)
            {
                return ex.Message;
            }
            return ret;
        }
求救高人指点下。