Ever get an error like this when running an apt update?

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B4D2D216F1FD7806

or

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://download.jitsi.org stable/ InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B4D2D216F1FD7806
W: Failed to fetch https://download.jitsi.org/stable/InRelease  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B4D2D216F1FD7806
W: Some index files failed to download. They have been ignored, or old ones used instead.

Happens.

Generally, this is quickly resolved by shockingly adding the public key. Which unless your memory is google-like, you probably need to google it… which may even be how you ended up here.

Anyway, here’s the command to get the key.

apt-key adv --keyserver hkps://keys.openpgp.org --recv-keys [KEY]

So, in our example with Jitsi’s key of B4D2D216F1FD7806 you would just run:

apt-key adv --keyserver hkps://keys.openpgp.org --recv-keys B4D2D216F1FD7806

Hope that helps. Remember, always be kind.