PayPal express checkout returning response as html in MVC .net

Question

I had test application integrated with Paypal express checkout and it was running fine. But now there seems some issue. After successful payment on paypal when my IPN handler check for response paypal returns response as html page instead of "VERIFIED" OR "INVALID" and because of this I'm not able to verify the payment. Is there any change in Paypal recently for express checkout? Below is complete code

<form id="Paypal" name="Paypal" action="https://www.sandbox.paypal.com/cgi-bin/webscr"
    method="post">
    @Html.Hidden("cmd", "_xclick")
    @Html.Hidden("business", "[email protected]")
    @Html.Hidden("item_name", "Payment for course registration")
    @Html.Hidden("amount", 100 )
    @Html.Hidden("no_shipping", "1")
    @Html.Hidden("return", "http://localhost:49319/cart/IPN")
    @Html.Hidden("rm", "2")
    @Html.Hidden("notify_url", "http://localhost:49319/cart/IPN")
    @Html.Hidden("cancel_return", "http://localhost:49319/cart/PaymentFailure")
    @Html.Hidden("currency_code", "CAD")
    @Html.Hidden("tax_cart", "1")
    @Html.Hidden("custom", "12")
    <div class="checkout-button">
        <input type="image" src="https://www.paypal.com/en_US/i/btn/btn_xpressCheckout.gif"
            align="left" style="margin-right: 7px;" />
    </div>
    </form>

IPN handler code:

 string paypalUrl = useSandbox ? "https://www.sandbox.paypal.com/cgi-bin/webscr"
            : "https://www.paypal.com/cgi-bin/webscr";


        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(paypalUrl);

        // Set values for the request back
        req.Method = "POST";
        req.ContentType = "application/x-www-form-urlencoded";

        byte[] param = Request.BinaryRead(Request.ContentLength);
        string strRequest = Encoding.ASCII.GetString(param);

        StringBuilder sb = new StringBuilder();
        sb.Append(strRequest);

        foreach (string key in formVals.Keys)
        {
            sb.AppendFormat("&{0}={1}", key, formVals[key]);
        }
        strRequest += sb.ToString();
        req.ContentLength = strRequest.Length;

        //for proxy
        //WebProxy proxy = new WebProxy(new Uri("http://urlort#");
        //req.Proxy = proxy;
        //Send the request to PayPal and get the response
        string response = "";
        using (StreamWriter streamOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII))
        {

            streamOut.Write(strRequest);
            streamOut.Close();
            using (StreamReader streamIn = new StreamReader(req.GetResponse().GetResponseStream()))
            {
                response = streamIn.ReadToEnd();
            }
        }

        return response;

Edit: Here is request string sent to Paypal

CONTEXT=wtgSziM4C5x0SI-9CmKcv2vkSeTLK5P_g6HqzC__YTYkcqziFNcB84p79Ja&myAllTextSubmitID=&cmd=_flow&transaction_subject=12&txn_type=web_accept&payment_date=01%3A59%3A21+May+02%2C+2011+PDT&last_name=User&residence_country=CA&pending_reason=paymentreview&item_name=Payment+for+course+registration&payment_gross=&mc_currency=CAD&business=pramod_1298956597_biz%40sumerusolutions.com&payment_type=instant&protection_eligibility=Ineligible&payer_status=verified&verify_sign=Ag7LtkvrF1u9.1ScLJwRM4btR1G1A16qsCs-xUl6EpI1rE1UWpodXJsc&txn_id=15Y20623GD922445F&payer_email=pramod_1298961722_per%40sumerusolutions.com&tax=0.00&test_ipn=1&first_name=Test&receiver_email=pramod_1298956597_biz%40sumerusolutions.com&quantity=1&payer_id=Z2MRT3Q9L6E28&receiver_id=RT3M59WESZHEE&item_number=&payment_status=Pending&handling_amount=0.00&shipping=0.00&mc_gross=850.00&custom=12&charset=windows-1252&notify_version=3.1&merchant_return_link=click+here&form_charset=UTF-8CONTEXT=wtgSziM4C5x0SI-9CmKcv2vkSeTLK5P_g6HqzC__YTYkcqziFNcB84p79Ja&myAllTextSubmitID=&cmd=_flow&transaction_subject=12&txn_type=web_accept&payment_date=01%3A59%3A21+May+02%2C+2011+PDT&last_name=User&residence_country=CA&pending_reason=paymentreview&item_name=Payment+for+course+registration&payment_gross=&mc_currency=CAD&business=pramod_1298956597_biz%40sumerusolutions.com&payment_type=instant&protection_eligibility=Ineligible&payer_status=verified&verify_sign=Ag7LtkvrF1u9.1ScLJwRM4btR1G1A16qsCs-xUl6EpI1rE1UWpodXJsc&txn_id=15Y20623GD922445F&payer_email=pramod_1298961722_per%40sumerusolutions.com&tax=0.00&test_ipn=1&first_name=Test&receiver_email=pramod_1298956597_biz%40sumerusolutions.com&quantity=1&payer_id=Z2MRT3Q9L6E28&receiver_id=RT3M59WESZHEE&item_number=&payment_status=Pending&handling_amount=0.00&shipping=0.00&mc_gross=850.00&custom=12&charset=windows-1252&notify_version=3.1&merchant_return_link=click+here&form_charset=UTF-8&cmd=_notify-validate

Answer 1

Ok. After lot of trial and error and posting this issue in paypal forum I got my payment gateway working. Though I'm not really happy with the solution.The solution is use PDT and don't use IPN. The response I got from paypal support was "The Problem is that IPN is an additional Notification system and there is a little delay in it. So it is not 100% the perfect solution for an autoreturn Page."

Paypal suggested me to use PDT and it's working now. I'll put the steps here so that it may help someone who is also facing such issue:

1. Activate the "AutoReturn" and PDT feature in your PayPal Account. Steps: Login to your PayPal account click on Profile click on Website Payment Preferences set Auto Return to On enter a valid URL in the Return URL text box set Payment Data Transfer to on. Note down the PDT token displayed. scroll to the bottom of the page and click "Save"

2. Pass below parameters to paypal cmd, business, item_name, amount, return, currency_code, custom.

3. Change IPN handler code with PDT code, PDT code in my case is as below-

   string authToken, txToken, query; string strResponse;

       authToken = ConfigurationManager.AppSettings["PDTToken"];
   
       //read in txn token from querystring
       txToken = Request.QueryString.Get("tx");
   
   
       query = string.Format("cmd=_notify-synch&tx={0}&at={1}", txToken, authToken);
   
       // Create the request back
       string url = ConfigurationManager.AppSettings["PayPalUrl"];
       HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
   
       // Set values for the request back
       req.Method = "POST";
       req.ContentType = "application/x-www-form-urlencoded";
       req.ContentLength = query.Length;
   
       // Write the request back IPN strings
       StreamWriter stOut = new StreamWriter(req.GetRequestStream(), System.Text.Encoding.ASCII);
       stOut.Write(query);
       stOut.Close();
   
       // Do the request to PayPal and get the response
       StreamReader stIn = new StreamReader(req.GetResponse().GetResponseStream());
       strResponse = stIn.ReadToEnd();
       stIn.Close();            
   
       // If response was SUCCESS, parse response string and output details
       if (strResponse.StartsWith("SUCCESS"))
       {
   
       }