Kindly refer to the following link(s):
Expiation (fidya) for deliberately breaking the fast (misconception of fasting 60 days for deliberately breaking the fast)
A complete explanation about Fidya (expiation) for those who cannot fast
Skipped fasting due to negligence, now chronically ill, cannot fast, can I give Fidya
Should I make up the fasts that I missed during my non practicing days?