Is it permissible to accept compensation for the delayed payment of dues after selling a program, given that the original contract included a penalty for delay?

Imposing a financial penalty on a client for late installment payments is forbidden and usurious, thus it is impermissible to take it. As for the remaining debt, the principle is that it should be repaid with its equivalent, not its value, and it is not permissible to link it to price levels or inflation. However, the more authoritative opinion is to consider the value of the currency if there occurs severe deception or a collapse in its value, which causes significant harm to the creditor.