He did not fast Ramadan because he was undergoing chemotherapy; what should he do?

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Check below answers in case you are looking for other related questions:
Is there any other way to compensate for missed fasts due to pregnancy and breastfeeding apart from fasting those days at a later time?
Can he work at night and not fast by day because of taking medicine?

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Related Answers:
He works for the military– is it permissible for him not to fast in Ramadaan?
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Making Up Fasting for a Woman who's Pregnancy, Postpartum, and Breastfeeding Prevented her from Fasting
Is there any other way to compensate for missed fasts due to pregnancy and breastfeeding apart from fasting those days at a later time?
Can he work at night and not fast by day because of taking medicine?

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