Must a merchant who sells by installments pay zakat on his trade wealth upon the passing of a hawl (lunar year) on the principal amount, even though some of the sale installments have not yet been collected, which would result in paying zakat multiple times on the same money?

The correct method for calculating zakat on commercial stores is for the merchant to assess the value of the goods upon the completion of a full year (hawl), add it to the money they possess, and then pay one-quarter of one-tenth (2.5%) of the total value, provided it reaches the nisab (minimum threshold). Zakat is not demanded more than once a year, and it is not permissible to delay zakat beyond its due time, which is the completion of the hawl.