There were 2 of them, redirecting the users AFTER registration to a page where they have to buy a subscription. For sure one of them was buggy and the coder has closed his site. The other one is on
Graveyard.
But as I said, both were working AFTER registration. This is the normal way. How do you think that you can check if someone has paid or not if you don't have any data of him? I don't mean that is impossible. Nothing is impossible. Just is complicating. You must prepare a pre-registration form to collect at least an email address, then save this email in a seperate table etc etc.