HTTP请求PowerAutomate错误:”基础连接已关闭,发送时发生错误”

using System;
using System.IO;
using System.Net;
using System.Text;

//传入目标地址Url和Post的参数jsonParas，返回目标端口的响应返回值
public static string HttpRequestByPost(string Url, string jsonParas) {

  //设置服务属性
  ServicePointManager.Expect100Continue = true;
  ServicePointManager.CheckCertificateRevocationList = true;
  ServicePointManager.DefaultConnectionLimit = 100;
  ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;//这里设置了协议类型
  ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

  //创建一个HTTP请求
  string strURL = Url;
  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strURL);
  request.Method = "POST";
  request.ContentType = "application/json";
  request.Accept = "*/*";
  byte[] payload;
  string paraUrlCoded = jsonParas;
  payload = Encoding.UTF8.GetBytes(paraUrlCoded);
  request.ContentLength = payload.Length;

  //发送请求，获得请求流 
  Stream writer;
  try {
    writer = request.GetRequestStream();
  }
  catch (Exception) {
    writer = null;
    Console.Write("连接服务器失败!");
  }
  writer.Write(payload, 0, payload.Length);
  writer.Close();

  //获得返回值
  HttpWebResponse response;
  try {
    response = (HttpWebResponse)request.GetResponse();
  }
  catch (WebException ex) {
    response = ex.Response as HttpWebResponse;
  }
  Stream s = response.GetResponseStream();
  StreamReader sRead = new StreamReader(s);
  string postContent = sRead.ReadToEnd();
  sRead.Close();
  return postContent;

}

//设置服务属性
ServicePointManager.Expect100Continue = true;
ServicePointManager.CheckCertificateRevocationList = true;
ServicePointManager.DefaultConnectionLimit = 100;
ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;//这里设置了协议类型
ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

/*.net 4.0 设置：*/
 ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
/*.net 4.5 设置(只要写SecurityProtocolType能够点出来的属性就可以)：*/
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12|| SecurityProtocolType.Ssl3 || SecurityProtocolType.Tls11 || SecurityProtocolType.Tls;