What is the ruling on working in installment sales (loan) offices that issue loans in the form of a commodity, whether the type of commodity is mentioned in the contract or not, and is there a sin upon one who leaves the space for the commodity blank in the contract at the request of the office owner?

Installment sales are permissible if the seller genuinely owns the commodity before selling it. The price and method of payment must be determined in the contract. It does not matter if the installment price is higher than the cash price. A condition for this is that the sale should not merely be a cover for an interest-based loan, meaning the seller pays the price of the commodity on behalf of the buyer and then reclaims the price from him with an increase. The permissibility of the transaction is not affected if the buyer does not intend to use the commodity but rather wants to sell it to benefit from its price (the issue of tawarruq). Therefore, if the office's work is installment selling in accordance with Sharia (definition) guidelines, then there is no harm. However, if it lends money with an increase, then this is forbidden usury (riba).