var verificationResponse = string.Empty;

            try
            {

                var verificationRequest = (HttpWebRequest)WebRequest.Create("https://ipnpb.sandbox.paypal.com/cgi-bin/webscr?cmd=_notify-validate");
                //var verificationRequest = (HttpWebRequest)WebRequest.Create("https://ipnpb.paypal.com/cgi-bin/webscr?cmd=_notify-validate");
                verificationRequest.Method = "get";
                verificationRequest.ContentType = "application/x-www-form-urlencoded";
                var streamIn = new StreamReader(verificationRequest.GetResponse().GetResponseStream());
                verificationResponse = streamIn.ReadToEnd();
                streamIn.Close();
                Response.Write(verificationResponse);
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }