httpClient PostAsJsonAsync 在 Framework 4.6 中不工作

Question

我不知道它是什么，但是当我在调试模式下运行我的项目并点击这条线时：

 var response = await httpClient.PostAsJsonAsync(url, payload);

它挂起一秒钟，然后就消失了，没有响应值。而且它也没有达到我的异常。

private async Task<string> PingServerAsync(DICOMClient client)
    {

        EchoViewModelSettings payload = new EchoViewModelSettings();
        payload.ClientAE = client.ClientAETitle;
        // more props here..            
       
        using (httpClient)
        {
            httpClient.BaseAddress = new Uri(m_appConfig.DICOM_URL);
           
            var requestUri = handler + "/Echo?SessionID=" + System.Web.HttpUtility.UrlEncode(session.SessionID.ToString());

            try
            {
                MqttService.applog.Debug($"Make request: {requestUri}");

                var url = "http://localhost/MyDicomAPI/api/dicom/Echo?SessionID=my_session";

                // *** FIRE POST HERE ***
                var response = await httpClient.PostAsJsonAsync(url, payload);                    

                MqttService.applog.Debug($"The Response: {response.Content}");

                if (response.IsSuccessStatusCode)
                {
                    var echoResponse = await response.Content.ReadAsStringAsync();
                    MqttService.applog.Debug($"The Echo Response is: {echoResponse}");
                }                    
                if (response.StatusCode == System.Net.HttpStatusCode.OK)
                {
                    Console.WriteLine(response.StatusCode.ToString());
                    return response.StatusCode.ToString();
                }
                else
                {
                    return response.StatusCode.ToString();
                }
            }
            catch (Exception ex)
            {
                MqttService.applog.Error($"WTF is wrong now: {ex}");
                throw;
            }
            
            
        }
    }

同时查看此视频教程作为参考 - https://www.youtube.com/watch?v=VSAlIE2SFHw