To what extent is it permissible to deal with a website that delivers funds to websites that do not accept Visa or Mastercard, in exchange for a commission on the amount paid?

Regarding intermediary websites between a client and a seller: if they are independent and issue visas, then the ruling on dealing with them is the same as the ruling on credit cards. However, if their work is limited to transferring money between the two parties for a known fee that they take from the buyer, then there is no objection to dealing with them. But if these websites pay the seller money and reclaim it with an increase from the buyer, then it is not permissible to deal with them because it is usury (riba).