Yep but if you want to support other payment types, such as paypal then you need to deal with that too. Suddenly you need to write payment abstractions on your

Yep but if you want to support other payment types, such as paypal then you need to deal with that too. Suddenly you need to write payment abstractions on your back-end to handle both and most pre-written libraries that try to do this fail because they don't handle cases you may need. That only handles the mechanics of accepting a payment too.