C# HttpRequest基礎連接配接已經關閉: 接收時發生意外錯誤

string rust="123344" ;

 Dictionary<string, string> dic = new Dictionary<string, string>();

            dic.Add("grant_type", "client_credentials");

            dic.Add("scope", "write");

            string token = Postsql("https://xxxxxxx", dic, rust);

 /// <summary>

        /// 指定Post位址使用Get 方式擷取全部字元串

        /// </summary>

        /// <param name="url">請求背景位址</param>

        /// <returns></returns>

        public static string Postsql(string url, Dictionary<string, string> dic, string token)

        {

            string result = "";

            ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;//SecurityProtocolType.Tls1.2;

            ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

            ServicePointManager.CheckCertificateRevocationList = false;

            ServicePointManager.Expect100Continue = false;

            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

            req.KeepAlive = false;

            req.ProtocolVersion = HttpVersion.Version11;

            //HttpWebRequest request = new HttpWebRequest();

            增加下面兩個屬性即可

            //request.KeepAlive = false;

            //request.ProtocolVersion = HttpVersion.Version10;

            req.Method = "POST";

            req.ContentType = "application/x-www-form-urlencoded";

            req.Headers.Add("Authorization",

                "Basic " + token);

            #region 添加Post 參數

            StringBuilder builder = new StringBuilder();

            int i = 0;

            foreach (var item in dic)

            {

                if (i > 0)

                    builder.Append("&");

                builder.AppendFormat("{0}={1}", item.Key, item.Value);

                i++;

            }

            byte[] data = Encoding.UTF8.GetBytes(builder.ToString());

            req.ContentLength = data.Length;

            using (Stream reqStream = req.GetRequestStream())

            {

                reqStream.Write(data, 0, data.Length);

                reqStream.Close();

            }

            #endregion

            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

            Stream stream = resp.GetResponseStream();

            //擷取響應内容

            using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))

            {

                result = reader.ReadToEnd();

            }

            return result;

        }