Go to EShop -> Plugins -> Payments, then click on os_creditcard to edit it Offline Credit Card Processing payment method is used if you want to collect the credit card information from the customer and make the payment by yourself. So when placing an order, if customer choose the Offline Credit Card Processing as the payment method, then they must enter CVV, Expired Date and Card Number to send them to admin's store to process payment. With Card Number, the system only store the 12 first digits to the database, 4 last digits will be send to the admin's store in the notification email. So after receiving the order, admin's store will go to the order details at the back-end side to get the 12 first digits, then merge them with 4 last digits that he received via email to have the full of 16 digits of Card Number. Only admin's store is able to know full of Card Number so it is secure.
Payment Fee = Payment Fee (Fixed amount) + Payment Fee (Percentage) * SubTotal / 100