Ohh, we spent aaaages yesterday trying to set up my brother's old iPhone for my dad. All the OTPs failed, even though we wrote them correctly. His iCloud didn't

Ohh, we spent aaaages yesterday trying to set up my brother's old iPhone for my dad. All the OTPs failed, even though we wrote them correctly. His iCloud didn't want to log in and resetting the password (as we thought we had the wrong one) just left everything in limbo. Apple support were less than helpful.