Asp.net Web API不响应响应

我正在使用ASP.NET核心中的WEB API。我得到了结果。但突然间我得到了一个例外 System.AggregateException:'值''无效。ameters=[{parameters}]，CommandType='{commandT''

SocketException:远程主机强制关闭了现有连接。 IOException:无法从传输连接读取数据：远程主机强制关闭了现有连接。。 HttpRequestException:将内容复制到流时出错

这是我的密码

        {
            string responseXML = string.Empty;
            try
            {
                System.Net.Http.HttpClient httpClient = new System.Net.Http.HttpClient { Timeout = new TimeSpan(0, 0, 500) };
                var eP = "EndpointBAseURL" + url;
                httpClient.BaseAddress = new Uri(eP);
                httpClient.DefaultRequestHeaders.Accept.Clear();
                httpClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
                System.Net.Http.StringContent content = new System.Net.Http.StringContent(requestData, System.Text.Encoding.UTF8, "application/json");
//Exception Happens in the following Line
                System.Net.Http.HttpResponseMessage response = httpClient.PostAsync(eP,content).Result;
               
                if (response.IsSuccessStatusCode)
                {
                    responseXML = response.Content.ReadAsStringAsync().Result;
                }
            }
            catch (WebException webEx)
            {
                responseXML = null;
                WebResponse response = webEx.Response;
                Stream stream = response.GetResponseStream();
                String responseMessage = new StreamReader(stream).ReadToEnd();
                //return responseMessage;
            }
            return responseXML;
        }