Is a contract for the purchase of an apartment under construction, which stipulates that the owner must pay an additional amount for the apartment's lifelong maintenance, Islamically valid, and what are the implications if it is not valid, knowing that the contract's payments and installments, including the maintenance fee, have already commenced?

It appears that the described transaction is a manufacturing contract (Istisna'a), which is binding on both parties if its conditions are met, namely: clear specification of the type, kind, quantity, and characteristics of the manufactured item, known price, and a defined deadline if applicable. The customer (Mustasni') has the option to reject the item if it deviates from the specifications. It is permissible to set a known period for guaranteeing manufacturing defects or maintenance. However, contracting for lifetime maintenance is not permissible due to the presence of ignorance (Jahala) and uncertainty (Gharar). Therefore, this contract must be annulled or corrected by specifying a known duration for the maintenance period.