Should the brother pay back one-third of the current value of the property upon repayment, or should he pay the amount previously agreed upon (3.5 million Syrian Pounds), regardless of the currency's collapse?

Selling at an unknown price is impermissible due to the element of gharar (uncertainty), and specifying the price is a condition for the validity of a sale. If the value of the apartment, which was named as the price for the land, was not explicitly mentioned in the contract, then it is an unknown price, and the sale is void. This is because the exact price of an apartment before its construction is complete cannot be known due to changing prices and market fluctuations. Ignorance of the price leads to the invalidation of the sale, as one of the conditions for a valid sale is knowledge of the price. Issues of dispute should be referred to the Sharia courts or discussed directly with scholars by both parties to the claim.