drooh - 9:11 pm on Jan 25, 2012 (gmt 0)

I am wondering if I can use paypal to return some kind of variable and check that a payment was made.

In my situation, a person on my site subscribes to login and watch videos. When they pay at paypal, I need it to return them to my site and allow them to create a username & password. But I am wondering how it my site will know if there was actually a transaction? Is there some sort of authorization key?