Together these let you pass a percentage surcharge on to customers for certain payment methods. Payment Gateway - Fee Applied % is the percentage added to the order, and Payment Gateway - Fee Applied to selects which methods it applies to (Digital Wallet, Stripe, Vantiv, Cash, Check, Stripe Terminal). For example 3% applied to Stripe adds a 3% fee line when the customer pays by card but not when they pay cash. Both are in the Payment group and configured by Sprwt; check local rules on card surcharges before asking for it to be enabled.