When having an older Tarsnap package you can get the following error:
Err:12 http://pkg.tarsnap.com/deb/focal ./ Release.gpg
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY ######
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W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://pkg.tarsnap.com/deb/focal ./ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY ######
W: Failed to fetch http://pkg.tarsnap.com/deb/focal/./Release.gpg The following signatures couldn't be verified because the public key is not available: NO_PUBKEY ######How to solve it?
What did the trick for me was to reapply the first steps of the Debian guide:
https://www.tarsnap.com/pkg-deb.html
Especially, the part of the initial setup tab.
When running that and then running: sudo apt-get update, it seemed to be working again.
You might run into this warning
W: Target Packages (Packages) is configured multiple times in /etc/apt/sources.list.d/tarsnap.list:1 You can solve it by editing: /etc/apt/sources.list.d/tarsnap.list and removing the first line.
Did you solve it is well? Let us know in the comments.