钉钉 返回文本非success 71009企业接入注册回调URL

有人帮我看看吗？ 公司想把通讯录回调事件放在钉钉上跑，感觉文档有些乱，这两天好不容易懂得什么意思了，可是注册回调的时候一直返回71009文本非success。看了很多回答好像都没有具体解决，有没有大佬可以帮忙看看？小官可以帮忙回答下吗？下面是我的代码……


string token = ConfigurationManager.AppSettings["DingDing.Token"];
            string encodingAESKey = ConfigurationManager.AppSettings["DingDing.EncodingAESKey"];
            string mSuiteKey = ConfigurationManager.AppSettings["DingDing.CorpId"];


            //url中的签名
            string msgSignature = Request["signature"];
            //url中的时间戳
            string timeStamp = Request["timestamp"];
            //url中的随机字符串
            string nonce = Request["nonce"];
            //查看post的内容
            string encryptStr = GetPostParam();


            //构造DingTalkCrypt
            DingTalkCrypt dingTalk = new DingTalkCrypt(token, encodingAESKey, mSuiteKey);
            //解密后的原文
            string plainText = "";
            //解密
            dingTalk.DecryptMsg(msgSignature, timeStamp, nonce, encryptStr, ref plainText);
            Hashtable tb = (Hashtable)JsonConvert.DeserializeObject(plainText, typeof(Hashtable));
            string eventType = tb["EventType"].ToString();


            switch (eventType)
            {
                case "user_add_org"://通讯录用户增加 do something
                    break;
                case "user_modify_org"://通讯录用户更改 do something
                    break;
                case "user_leave_org"://通讯录用户离职  do something
                    break;
                default:
                    break;
            }
            string encrypt = "";
            string signature = "";
            string res = "success";
            dingTalk = new DingTalkCrypt(token, encodingAESKey, mSuiteKey);
            //加密，对"success"字符串加密
            dingTalk.EncryptMsg(res, timeStamp, nonce, ref encrypt, ref signature);
            Hashtable jsonMap = new Hashtable
                {
                    {"msg_signature", signature},
                    {"encrypt", encrypt},
                    {"timeStamp", timeStamp},
                    {"nonce", nonce}
                };
            string result = JsonConvert.SerializeObject(jsonMap);
            Response.Write(result);