Fidya – Kaffara is in lieu of fasting.
For example, if a person is not able to fast due to sickness and the sickness continues till the next month of Holy Ramadhan they are required to pay Fidya.
Fidya or Kaffara is also mandatory if a person was not able to fast due to traveling or sickness. However, the person recovered from illness but was unable to make up the fast until next holy month of Ramadhan. In this scenario, a person is required to pay Fidya Kaffara as well as make-up for the fast.
For those who are of old age or cannot fast due to deteriorating health, they are only required to give Fidya every year.