Как использовать restful service в настольном приложении

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мы получили ошибку ниже
Базовое соединение было закрыто: произошла непредвиденная ошибка при приеме.

Что я уже пробовал:

var request = (HttpWebRequest)WebRequest.Create(EndPoint);

request.Method = Method;
request.ContentLength = 0;
request.ContentType = contentType;
request.Timeout = 600000;
request.KeepAlive = false;

request.UseDefaultCredentials = true;
request.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials;
request.Method = WebRequestMethods.Http.Post.ToString();
request.Credentials = new NetworkCredential(username, password);


if (Method == "POST")
{
    object input = new
    {
        firstName = "a",
        LastName = "b",

    };
    string inputJson = (new JavaScriptSerializer()).Serialize(input);
    byte[] bytes = System.Text.Encoding.ASCII.GetBytes(inputJson);
    request.ContentLength = bytes.Length;
    System.IO.Stream os = request.GetRequestStream();
    os.Write(bytes, 0, bytes.Length);
    os.Close();
}
using (var response = (HttpWebResponse)request.GetResponse())// request.address changes at this line on "POST" method types
{
    var responseValue = string.Empty;

    if (response.StatusCode != HttpStatusCode.OK)
    {
        var message = String.Format("Request failed. Received HTTP {0}", response.StatusCode);
        throw new ApplicationException(message);
    }

    // grab the response
    using (var responseStream = response.GetResponseStream())
    {
        if (responseStream != null)
            using (var reader = new StreamReader(responseStream))
            {
                responseValue = reader.ReadToEnd();
            }
    }

    return responseValue;
}

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