What is the ruling on using shopping vouchers that are distributed as rewards (at a rate of 1% of the value of purchases) when using a credit card, knowing that no interest is calculated on the card?

Credit cards are permissible under two conditions: that the issuer does not charge more than their actual cost, and that they do not include a late payment penalty. As for the vouchers granted upon purchase with a credit card, they fall under commercial incentives, and are permissible under two conditions: that the fees charged for card services are based on the actual cost, and that the card is used out of necessity, not solely to anticipate the prize. If the price of the commodity is its true price and was not inflated for the sake of the prize, and the person did not purchase the commodity solely to anticipate the prize, then there is no harm in that.