### Having trouble in use of apt-get update?

If you get an error like this: GPG-Fehler:
http://debian.fhem.de/ / Release: [...] NO_PUBKEY xxxxxxxx

Try the following steps:
- Find the old gpg key
  `sudo apt-key list
  pub 2048R/BF0E6825 2014-10-05 [verfällt: 2024-10-02]
  uid "..." (betateilchen) <repo@betateilchen.de>`
- Delete the old key identified in previos step
  `sudo apt-key del BF0E6825`
- Import new gpg key
  `wget -qO - http://debian.fhem.de/archive.key | sudo apt-key add -`
- Check result
  `sudo apt-key list
  pub 4096R/CC0B9B66 2016-12-26 [verfällt: 2021-12-25]
  uid betateilchen (debian.fhem.de) <gpg@betateilchen.de>`