What is the ruling on late payment fees in installment sales, leasing, and construction contracts, how are they handled, and what is the ruling on those who work with them, knowing that their legal nature does not allow for their alteration?

If the two parties to the contract can stipulate that the value of the interest be zero, then this is what must be done. It is not permissible to conclude a contract that stipulates late payment interest, except out of necessity or a recognized need. The debtor must adhere to the repayment time, and the creditor must avoid late payment interest, due to its unlawfulness. It is not permissible to work in writing or documenting these contracts except out of necessity or a need that is equivalent to it, while searching for permissible work.