Is it obligatory to make up for a day of fasting that one who made a vow broke without a legitimate Shar'i excuse, in addition to fasting a day in its place?

Fasting a vow is obligatory, and it is not permissible to break it without a valid Shar’i (Islamic legal) excuse, due to the Almighty’s saying: “And do not invalidate your deeds.” Natural hunger is not an excuse; therefore, one must repent and make up the day.