从控制台应用程序调用Web服务时出现内部服务器错

我创建了一个Web API，我想要从外部应用程序调用Web服务，如控制台。但我收到内部服务器错误。

private void CallWebService()
    {  string licenseResposeJSON = string.Empty;
        string value = " http://vyastestapi1.azurewebsites.net/api/Employee/POSTaccount";     
                try
                {
            {
                using (WebClientEx client = new WebClientEx())
                {    
                       client.Timeout = 6000000;
                    client.Headers.Add(HttpRequestHeader.ContentType, "application/json");
                    licenseResposeJSON = client.UploadString(value.ToString(), "  vaishali");
                    }
                    Console.WriteLine("Name" + licenseResposeJSON);
                    Console.ReadLine();    
            }    
                }
                catch (WebException exception)
                {
                    string str = string.Empty;
                    if (exception.Response != null)
                    {
                        using (StreamReader reader =
                            new StreamReader(exception.Response.GetResponseStream()))
                        {
                            str = reader.ReadToEnd();
                        }
                        exception.Response.Close();
                    }
                        if (exception.Status == WebExceptionStatus.Timeout)
                    {
                        throw new InvalidPluginExecutionException(                                "The timeout elapsed while attempting to issue the request.", exception);
                    }
                   }                  }        
    public class WebClientEx : WebClient
    {   public int Timeout { get; set; }
            protected override WebRequest GetWebRequest(Uri address)
        {                var request = base.GetWebRequest(address);
            request.Timeout = Timeout;
            return request   }}

错误：