[kh99]

I don't have any experience adding payment api, but I think I understand the basics - go to "Add New Payment API" under "Paid Subscriptions", enter your info. If you enter, for example, clickbank in the "Classname" field, then you need to create a file in includes/paymentapi called class_clickbank.php. Probably the thing to do is copy one of the other "class_" files and replace it's class name (ccbill, for example) with clickbank everywhere it appears in the code. Then the hard part, you need code to implement your api.

Anyway, hopefully that's some help and not just the obvious parts .