Is it obligatory to make up for the days of Ramadan in chronological order (for example, the year 1440 then 1439), and does the fast become void by making up for one Ramadan before making up for another?

Scholars differ on the obligation of observing sequence when making up missed fasts from past Ramadans, holding two views:

First: The obligation of observing sequence. This is the view of the Hanbalis. Second: No obligation to observe sequence. This is the preferred view among the Hanafis and the view of the Malikis.

The Permanent Committee has issued a fatwa stating the obligation of observing sequence for making up missed fasts. Thus, one should make up the days missed from the first month, then the second, and so on. For delaying the makeup fast beyond its time, one must feed a poor person for each day.

Observing sequence is more cautious. However, if someone was unaware of the sequence or forgot it and made up their missed fasts, their makeup fast is valid, and there is no blame on them. If someone delays making up their missed fasts from Ramadan until the next Ramadan begins without a valid excuse, then in addition to making up the fasts, they must pay an expiation (fidyah) by feeding a poor person for each day.