What is the ruling on purchasing an apartment from a company that sells it in installments with an 8% monthly increase, on the condition that a down payment is made and the remainder is paid in monthly installments, knowing that the company deals with the bank and the buyer deals with the company?

Installment sales of apartments are permissible if the price is fixed and known to both parties and is not subject to increase even if payment is delayed. However, if interest is calculated on installments and delayed payments separately from the price, this is a usurious transaction, prohibited between the buyer and the company, or between the company and the bank. This transaction is not permissible for the buyer because it causes the company to fall into what is unlawful.