代码如下所示：

protected string PostRequestAsync(string uri, dynamic payload, string ContentType = "application/json") 
        {
            var result = "";
            //处理Https
            var handler = new HttpClientHandler();
            handler.AllowAutoRedirect = true;
            System.Net.ServicePointManager.SecurityProtocol =  SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
            handler.ServerCertificateCustomValidationCallback = (sender, cert, chain, sslPolicyErrors) => { return true; };
            //构建请求
            using (var httpClient = new HttpClient(handler)) 
            {
                //20秒响应时间
                httpClient.Timeout = new TimeSpan(0, 0, 0, 20);
                HttpResponseMessage message = null;
                try
                {
                    //将请求payload序列化
                    var payloadString = JsonHelper.Serialize(payload);
                    HttpContent content = new StringContent(payloadString);
                    //httpClient.DefaultRequestHeaders.Add(HttpClientSession.TokenName, HttpClientSession.Token);
                    content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(ContentType);
                    var plateformPostUrl = HttpClientSession.PlateformUrl+uri;
                    var response =  httpClient.PostAsync(plateformPostUrl, content);
                    message = response.Result;
                    //如果返回码为200认为成功并返回结果
                    //如果Body内的code为500也认为成功，但要在业务中进行处理
                    if (message != null && message.StatusCode == System.Net.HttpStatusCode.OK)
                    {
                        result = message.Content.ReadAsStringAsync().Result;
                    }
                    else
                    {
                        throw new Exception($"code:{message.StatusCode},message:{message.Content.ReadAsStringAsync().Result}");
                    }
                }
                catch (Exception ex)
                {
                    throw new Exception(ex.Message);
                }
            }
            return result;
        }

为什么会抛这个异常呀，这个方法是我在网上学到的