Is it permissible for a Muslim who is fasting to make up for missed days of Ramadan to break his fast without a legitimate excuse, and what are the legitimate excuses that permit breaking the fast?

A Muslim is not permitted to break a mandatory fast that has been initiated, such as a fast to make up for Ramadan, a votive fast, or an expiatory fast, except for a legitimate Shari excuse. Otherwise, they would be sinful. The legitimate Shari excuses here are those that permit breaking the fast in Ramadan, such as: severe illness, travel, menstruation and postpartum bleeding, and pregnancy and breastfeeding if the pregnant or nursing woman fears for herself or her child. The understanding of the Prophet's (peace and blessings be upon him) statement to Umm Hani: "It does not harm you if it was voluntary" indicates that breaking an obligatory fast is harmful and sinful.