If the store has chosen to pass card-processing costs to the customer (rather than absorbing them, which is the default) under Business: Cart > Processing: Stripe Charged to, a Processing Fee percentage is added on top of whatever you're paying by card (not on the portion covered by your Digital Wallet balance). It only applies to Stripe/Stripe Terminal payments. The rate can include a cross-border surcharge if the store's payout country is flagged as cross-border, and is reduced if you're paying in person on a Stripe Terminal reader.