paypal ipn integration in asp.net application - asp.net

Question

Iam trying to integrate paypal ipn in my application,but Iam getting error like "An exception of type 'System.Net.WebException' occurred in System.dll" but was not handled in user code in streamwriter.I have tried the below code.Please suggest.
using System;
using System.IO;
using System.Text;
using System.Net;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Net.Mail;
public partial class ipn : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
//Post back to either sandbox or live
string strSandbox = "https://www.sandbox.paypal.com/cgi-bin/webscr";
string strLive = "https://www.paypal.com/cgi-bin/webscr";
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(strLive);
//Set values for the request back
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
byte[] param = Request.BinaryRead(HttpContext.Current.Request.ContentLength);
string strRequest = Encoding.ASCII.GetString(param);
strRequest += "&cmd=_notify-validate";
req.ContentLength = strRequest.Length;
//Send the request to PayPal and get the response
StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
streamOut.Write(strRequest);
streamOut.Close();
StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
string strResponse = streamIn.ReadToEnd();
streamIn.Close();
if (strResponse == "VERIFIED")
{
//check the payment_status is Completed
//check that txn_id has not been previously processed
//check that receiver_email is your Primary PayPal email
//check that payment_amount/payment_currency are correct
//process payment
}
else if (strResponse == "INVALID")
{
//log for manual investigation
}
else
{
//log response/ipn data for manual investigation
}
}
}

Answer 1

string Identity_Token = "zkiMk_t - XXXXXagbIDrzPAChXuWIYVS66TXXXXXXXXXXXXXXXXXXXXXXXXXX";//From you paypal account
string txToken = Request.QueryString["tx"];
string query = string.Format("cmd=_notify-synch&tx={0}&at={1}", txToken, Identity_Token);
string strLive = "https://www.paypal.com/cgi-bin/webscr";
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(strLive);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
byte[] param = Request.BinaryRead(HttpContext.Current.Request.ContentLength);
string strRequest = Encoding.ASCII.GetString(param);
strRequest += query;
req.ContentLength = strRequest.Length;
//Send the request to PayPal and get the response
StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
streamOut.Write(strRequest);
streamOut.Close();
StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream());
string strResponse = streamIn.ReadToEnd();
streamIn.Close();
// If response was SUCCESS, parse response string and output details
if (strResponse.StartsWith("SUCCESS"))
{
Label1.Text = "OK";
}
else
{
Label1.Text = "NO";
}
}
}