Is zakat due on a sum of money paid as the price for aملك clinic that will be received two years from the date of payment?

As long as you have paid the price to the seller, there is no Zakat (definition) due on the apartment, because it has exited your ownership. However, if the contract was void due to the absence of the conditions for an Istisna' contract (such as knowledge of the price, the object, and the deadline), then the money still remains your property, and you should seek to reclaim it. Zakat is not obligatory on it until you take possession of it. If you do take possession of it, then you must pay Zakat on it for the past years.