Must one make up for the day on which a fasting person ate, thinking it was the Maghrib call to prayer, but then it became clear to him that the Maghrib had not yet been called?

Some scholars are of the opinion that whoever resolves to break their fast has invalidated it. However, Sheikh Ibn Uthaymeen favored the view that the fast remains valid in such a case. Therefore, your fast is valid as long as you did not swallow any part of the date. If you did swallow something, thinking that the sun had set, scholars have differed on whether the fast is invalidated. The view that the fast remains valid is a strong one, but it is more cautious to make up that day to avoid disagreement.