HTTP POST：基础连接 : 连接被意外关闭

HttpPost 报错 System.Net.WebException: 基础连接 : 连接被意外关闭

调用失败：System.Net.WebException: 基础连接已经关闭: 连接被意外关闭。
在 System.Net.HttpWebRequest.GetRequestStream(TransportContext& context)
在 System.Net.HttpWebRequest.GetRequestStream()
在 WCS.Common.Util.CSHttpHelp.HttpPost(String postUrl, String postBody)
在 Client.Call(String action, String floor, Int32 type)

postman可以正常访问，各种方法都尝试了，都不行

代码如下：

public static string HttpPost(string postUrl, string postBody)
          {
            System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(postUrl);
            request.ContentType = "application/json";
            request.Method = "POST";
            request.Timeout = 300000;
            request.KeepAlive = false;
            request.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore);
            byte[] buffer = System.Text.Encoding.UTF8.GetBytes(postBody);
            request.ContentLength = buffer.Length;
            request.GetRequestStream().Write(buffer, 0, buffer.Length);

            System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();
            using (System.IO.StreamReader myreader = new System.IO.StreamReader(response.GetResponseStream(), Encoding.UTF8))
            {
                return myreader.ReadToEnd();
            }
        }

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
ServicePointManager.SecurityProtocol = (SecurityProtocolType)192 | (SecurityProtocolType)768 | (SecurityProtocolType)3072;
你在WebRequest 请求之前加上这2句试试

不懂这个语言
是否可以抓包看看，看下http的交互的时候有什么异常，是否在这种异常下程序出了bug？
还有就是没有成功啥的

先确定你请求的接口返回是不是文本类型
StreamReader 单独try看看异常