Unable to update Plesk Obsidian 18.0.34 to the latest available build on Ubuntu 16.04: There is no release with ID ‘PLESK_18_0_35’ of product ‘plesk’ at the installation source

Symptoms

• Unable to update Plesk Obsidian to the latest version with the following error:

  Error: There is no release with ID 'PLESK_18_0_35' of product 'plesk' at the installation source

  ---

  Error: Unable to receive update information for the package(s)

• Notification with the error regarding the failed update is sent to Plesk admin over email:

  Some problems occurred with the System Updates tool on your server. Please resolve them manually.
  INFO: pum is called with arguments: ['--list', '--repo-info', '--json']
  W:The repository 'http://autoinstall.plesk.com/PHP73_17 xenial Release' does not have a Release file.
  W:Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
  W:See apt-secure(8) manpage for repository creation and user configuration details.
  E:Failed to fetch http://autoinstall.plesk.com/PHP73_17/dists/xenial/all/binary-amd64/Packages 404 Not Found
  E:Some index files failed to download. They have been ignored, or old ones used instead.
  ERROR: Exited with returncode 1.

Cause

Ubuntu 16.04 is installed on the server. Ubuntu 16.04 reached End-of-life on April 30th, 2021.
The latest supported version of Plesk Obsidian for Ubuntu 16.04 is 18.0.34, so no further Plesk updates are available.

Resolution

Apply one of the possible solutions:

• Migrate from the current Plesk server to a new one with one of the supported OSes installed.

• Perform a dist-upgrade from Ubuntu 16.04 to Ubuntu 18.04.