Must I make up the fast of the first day of Ramadan if I discover a brown spot of blood after performing ghusl and fasting half the day?

You must fast if the spot discovered after the cessation of menstruation and seeing one of the signs of purity is not menses, based on Umm Atiyyah's statement: "We used not to consider the yellowish and brownish discharge as anything," and "We used not to consider the yellowish and brownish discharge after purity as anything." You must make up the fast if you drank while ignorant of the ruling.