Unable to update Plesk with error: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY

Symptoms

• Unable to update Plesk on a Debian-like OS with the error below:

  W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://autoinstall.plesk.com/RUBY_0.0.2 buster InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BD11A6AA914BDF7E
  W: Failed to fetch http://autoinstall.plesk.com/RUBY_0.0.2/dists/buster/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BD11A6AA914BDF7E

• Plesk admin may receive an email with the following content:

  INFO: pum is called with arguments: ['--list', '--repo-info', '--json']
  ERROR:
  ERROR: Exited with returncode 1.

Cause

Plesk GPG key misconfiguration.

Resolution

1. Connect to the server via SSH.

2. Fetch and install the Plesk GPG key:

   # wget http://autoinstall.plesk.com/plesk.gpg && apt-key add plesk.gpg

3. Open the repository in question in any text editor, for example, in the vi editor:

   # vi /etc/apt/sources.list.d/plesk-ext-ruby.list

4. Add the missing signed-by section to the file as below:

   deb [arch=amd64 signed-by=/etc/apt/keyrings/plesk.gpg] http://autoinstall.plesk.com/RUBY_0.0.2 buster all

5. Save the changes and close the file. Re-run Plesk update if required.