What is the ruling on using the virtual "Al-Ruqi Mastercard" issued by American banks, which some liken to prepaid "Sawa" cards, to purchase goods online? Is it permissible, or might it lead to usury?

There is no objection to using pre-paid credit cards, and there is no harm in charging a fee for the service. It is permissible to make online purchases with them, except for items that require immediate physical possession, such as gold and silver. There is also no objection to the dollar exchange rate differing from the market rate, as long as there is immediate mutual possession. Caution should be exercised when dealing with untrustworthy entities.