Public key not available

[ghost]

System Details:

• Operating System:Linux
• Distro(For GNU/Linux and BSD users): MX Linux (Debian based)
• Desktop Environment(For GNU/Linux and BSD users):Xfce
• Persepolis Version: 3.0.0.2
• How do you install Persepolis? (Repositories, source, ...) From PPA repository
• Please attach log files if crash or paste error message

  Err:5 http://ppa.launchpad.net/persepolis/ppa/ubuntu groovy InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AC4E8D9CDCB0980D
  Reading package lists... Done
  W: GPG error: http://ppa.launchpad.net/persepolis/ppa/ubuntu groovy InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AC4E8D9CDCB0980D
  E: The repository 'http://ppa.launchpad.net/persepolis/ppa/ubuntu groovy InRelease' is not signed.
  N: Updating from such a repository can't be done securely, and is therefore disabled by default.
  N: See apt-secure(8) manpage for repository creation and user configuration details.

  Issue Description and steps to reproduce:

  1. Add PPA repo using add-apt-repository
  2. Gives out the warning and error messages above

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