Key Takeaways
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Save the backup codes somewhere safe
If you lose your phone, the backup codes are the only self-serve way back in. Each code signs you in once.
After your password, a Two-factor authentication screen asks for the code. Tick Trust this device for 30 days on your own computer or phone to skip it next time.

Lost your phone? Press Use a backup code instead and enter one of the saved codes. Then disable and re-enable 2FA with the new phone.

Settings → Account → Security → Disable, confirm with your password and a code, and it is off.
The code is rejected. Your phone's clock is off. Authenticator apps rely on exact time. Enable automatic time in the phone settings.
No phone and no backup codes. Email [email protected] from the account's email address. We verify identity manually and reset 2FA. This takes a working day.
I signed up with Google and there is no Enable button. Set a password first via Forgot password? on the sign-in page. Security options appear once the account has one.