Hello everyone,
I'm new to paypal and after reading this article http://www.codeproject.c...PalPaymentInASPNET.aspx
I'm trying to make it work in my website.

In the form I post to paypal with the details of the payment i specify both RETURN URL and NOTIFY_URL.

When I complete successufull the transaction on paypal server, and I click on the "return to the site" link, i'm redirect to the payment_success.aspx (RETURN URL parameter) page on my website.
This is a simple page to thank tha buyer for the purchase, and in the code behind I should check with paypal that everything is ok.
So I post to paypal all the variables I received adding "cmd=_notify-validate".

But I get always IPNResponse = INVALID.

I would like to understand why!!
And I'm also confused about this 2 pages [RETURN URL] page and [NOTIFY_URL] page.
Should I check the paymant in both pages?
I have exactly the same code behind for both pages

Thanks for all replies
Diego