Apple Watch Series 9 needs a safe reset or will not reset

The checks in more detail

After an erase you can restore from the backup, which brings back watch faces, apps and settings, or set up as new if you think a setting was the cause. On the Series 9, the double-tap gesture and its settings are restored too. Keep the watch on its charger during an erase, and expect the Apple logo for a while. A cellular watch asks whether to keep the plan. It helps to know what a restore brings back and what it does not: a backup restores watch faces, app layouts, settings and Health data stored on the watch,

but passcodes and some payment cards must be set up again, and Apple Pay cards need re-adding with the card's security code. Cellular plans need re-activating with the carrier if you removed them. Allow time for the iPhone to restore and the watch to sync apps, which can take longer than the initial pair. Apple Pay is worth planning for: when you unpair and erase, cards stored on the watch are removed, and when you restore you add them again by entering each card's details in the Wallet app on the iPhone. If you use transit cards or Express Mode, set them up again too.

Check that your Apple Account is signed in on the new pairing, and test a payment in a shop with a small purchase to confirm it works. Keep your iPhone's passcode handy, because the watch asks for it during setup. Before you erase, note any custom complications and watch faces you made, because a restore brings them back but a set-up as new does not; take screenshots of the faces you like. If you use third-party apps with their own accounts, such as workout or music services, expect to sign in again on the watch after a reset, so have the passwords available.