Preliminary Remarks
In Self Service in the snippet Subscriptions , customers can manage their payment method directly via their subscription.
Change or add payment method
Open snippet Subscriptions .
Click on Manage .
Click to Change .
Select from payment methods already created or add a new payment method (the payment methods set in the Merchant Backend under Payment Transactions appear here).
Select the subscription for which the new payment method is to be activated.
The customer can recognize the payment method that is currently activated for this subscription by the green tile.