What do you do if you forget to make niyyah for fasting before Fajr and don’t wake for suhur?
The Ramadan fast is invalid if niyya is missing, the latter being defined as intention formed anytime the previous night before the start of Fajr. One still has to fast that day regardless. Then one makes it up later as a qada‘ of that day of Ramadan.
Hajj Gibril Haddad