@Micha44
Hi, the issue happens when you try to enable 2FA or the 2FA has been enabled successfully but no verification code received via email when a new device tries to login?
Please refer to the steps below for troubleshooting:
1) Check your Spam or Junk folder.
2) Ensure that you are using the correct email account. Tap the three lines icon on Tether App and hit the Account Icon on the top left to verify it.
3) Add TP-Link email address ' no-reply@email.tp-link.com ' into Whitelisted email senders or Safe Senders as this FAQ
4) Ensure your phone is connected to the internet and your Tether App is up to date.
For more information related to 2FA on Tether App, please refer to this thread: Introducing Two-Factor Authentication (2FA) on Tether App