What is the ruling on taking a sum of money from a contractor as a concession for part of a flat's installment, to be paid as rent for another flat, due to the contractor's delay in handing over the flat, knowing that the contractor did not take an advance to benefit from it as a loan, but rather took it as an advance for a flat?

The expenditure in which the contractor pays monthly rent to the questioner when the apartment construction is not completed within a specified period, and the payment continues indefinitely, is an invalid agreement and leads to injustice against the contractor and the wrongful consumption of his wealth. The questioner is not entitled to compensation except for the actual damage incurred due to the contractor's delay in fulfilling his obligation, which should be determined by experts and fair arbitrators.