I can see the good in involving the tb in this. At the same time it is still a longer and more complicated way, when there is payment providers that set this up and then just chanrge the customer account and send the money to the merchant. Simple and clean but ofc limit the number of payment gateways. Another Question is how the customer see it. Do they trust he shop to stop the billing when the customer want? Or do they have more trust in Paypal where they easy stop it without involve the shop