Is it permissible to use an application that allows payment within 30 days without an increase, but charges a fee for extending the payment period if payment is not made within the specified time, while being careful to pay immediately upon receipt of the goods to facilitate returns?

The deferred price of a commodity is a debt that must be repaid in kind without any increase in exchange for delaying payment; otherwise, it would be usury (riba). Contracting with usury and consenting to it from the outset is impermissible. Therefore, it is not permissible to accept the usurious condition imposed by such applications. An uncovered credit card may not be issued or used if it stipulates an increase in usurious interest, even if the card applicant intends to pay within the free grace period.