Is Zakat obligatory on money that reached the Nisab and a Hawl (one lunar year) passed on it for years, then at the time of paying Zakat it did not reach the Nisab? And how can the time of paying Zakat be changed to the month of Ramadan if it is paid in another month?

Among the conditions for zakat is the passing of a full year (hawl) on the wealth, provided it reaches the nisab. If the wealth falls below the nisab during the year, then no zakat is due on it. If it reaches the nisab again, its hawl (zakat year) begins anew. Zakat becomes obligatory upon the completion of a full year from the time the wealth reached the nisab. It is not permissible to delay it in order to make its hawl coincide with Ramadan. However, it is permissible to pay zakat in advance before the completion of its hawl.