Besides PayPal, you can also pay to your affiliates in any other form of payment. Such as with Gift Cards, Discount Codes, Bank transfers, Offline Payments or in any other form of payment. So, if you have made commission payments in any such form, you can mark the commission as paid manually. Please note, that you will need to upload either a PDF or a screenshot as an evidence of the payment made. Your affiliate can see this proof in their dashboard.