Are the 2% fees imposed on foreign currencies in the bank's prepaid cards considered usury (riba), given that the total amount (item + fees) remains less than its price locally?

The bank acts as an agent for the client in prepaid cards, and it pays the purchase invoice from its own account. If the currencies differ, the bank converts the amount from the client's currency to the seller's currency, and it is permissible for the bank to take a known and fixed commission for this conversion.