Is it permissible to obligate the buyer to a new price for iron after its price has increased and he has delayed payment, knowing that he considers this usury (riba)?

It is religiously forbidden to increase the debt when the buyer delays payment, procrastinates, or when the price of the commodity rises in the market. Stipulating an increase or imposing a fine is considered forbidden usury (riba). A condition for the validity of a sale is that the price must be known at the time of the contract. Therefore, it is not permissible to agree that the price will be determined at the time of payment.