Linux Mint 20 PPA not signed

[Mark Krubsack]

Tried to install audio-recorder. Failed. Not signed. No public key.

Get:20 http://ppa.launchpad.net/audio-recorder/ppa/ubuntu focal InRelease [15.9 kB]
Err:20 http://ppa.launchpad.net/audio-recorder/ppa/ubuntu focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5CF12638ACF9669F
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net/audio-recorder/ppa/ubuntu focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5CF12638ACF9669F
E: The repository 'http://ppa.launchpad.net/audio-recorder/ppa/ubuntu focal 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.