Is buying online with a credit card that offers a special discount to its holders, while the price is higher for non-holders of this card, considered a usurious transaction? And what should be done if that is the case?

Using a credit card is permissible if it does not stipulate interest or a penalty for late payment, and if it does not charge a percentage for cash withdrawals that exceeds the actual fee. It is not permissible to purchase gold, silver, or currencies with an uncovered credit card. Discount offers linked to the use of a specific credit card are religiously permissible if the card itself is free from religious prohibitions.