Login to MyZyxel and access the account settings. Click the "Two-Factor Authentication" tab and click the Get New Backup Codes, this will generate 10 new codes. Copy them and store them in a reliable location.
I have not received the initial verification email with 6-digit code to enable the 2FA feature.
If you have not yet received the verification email to enable the 2FA feature click the "Send the verification instructions again" link at the bottom of the setup window.
Check your SPAM/JUNK inbox or set 'firstname.lastname@example.org' as a trusted sender.
Check for email later. If 'email@example.com' email account or the 'myzyxel.com' do domain have been added to trusted email filter your SMTP server should allow the message through. Unfortunately, we cannot control remote SMTP servers (Gmail, Hotmail/Outlook/Live, iCloud, Yahoo, etc.) so if the message is stuck in their filtering queue Zyxel cannot do anything about that to speed up the process so the message gets to your inbox quicker. Because this type of scenario is out of our control, we recommend using the authenticator app 2FA over email codes. The authenticator app will always have a code ready.
The 6-digit code, obtained via authenticator app or email, is not working.
Verify your device has the correct time (if your device has a manual time setup, change to sync to NTP server).
OTP tokens generated by the authenticator app are only good for 30 seconds. Wait for a fresh one to be generated and try using it within that 30 second window.
Use a backup code.
Select the option "Failed to get verification codes?". A new window will appear giving you the options to enter an OTP code from authenticator app, have a code emails to you, use a backup code or get help. Select the option to have a code emailed to you.
Contact Zyxel Technical support for additional support. Support is available Monday through Friday from 8AM to 5PM PT @ 800-255-4101 option 5. You can also get email support by completing the "Support Request Form" here.
Unable to scan the QR code to setup authenticator app.
If your device camera is having issue scanning the QR code, select the "Can't scan it?" option.
Once this option is selected a key code will be provided so you can add manually to your authenticator app.
Lost backup codes and/or device running authenticator app.
Login to your MyZyxel account.
When prompted for a verification code, enter 6 random digits (123456 for example).
When verification attempt errors out, click the “Failed to get verification codes?” and select the option to have one emailed to you.
Once you have successfully logged in, disable the 2FA.
Following the instructions on this guide to re-configure the 2FA method.