Unable to update Plesk or install system updates: The repository does not have a Release file

Symptoms

• Unable to update Plesk or install system updates, the process fails with the following error:
  

  PLESK_ERROR: ERROR: E:The repository 'http://ppa.launchpad.net/danmbox/ppa/ubuntu bionic Release' does not have a Release file.
  W:Updating from such a repository can't be done securely, and is therefore disabled by default.

Cause

The repository that is mentioned in the error is not available online or deprecated.

Resolution

1. Log into the server via SSH.
2. Using the URL of the repository mentioned in the error, find a file that contain the affected repository:
   

   # grep -ri "http://ppa.launchpad.net/danmbox/ppa/ubuntu" /etc/apt/ | grep -vE ":#|.save" | cut -d ":" -f1 | uniq

   The output will be similar to below:

   CONFIG_TEXT: /etc/apt/sources.list.d/ondrej-ubuntu-apache2-bionic.list

3. Using the vi text editor open files that were found in the previous step.
4. Comment the lines that contain repository from the error with the # symbol by changing it from:
   

   CONFIG_TEXT: deb-src http://ppa.launchpad.net/danmbox/ppa/ubuntu bionic main

   To

   CONFIG_TEXT: #deb-src http://ppa.launchpad.net/danmbox/ppa/ubuntu bionic main

5. Save the changes.
6. Try to upgrade Plesk one more time.