error installing plesk-ssh-terminal: useradd: group plesk-ssh-terminal exists

Symptoms

• Error installing the Plesk SSH Terminal:
  

  PLESK_ERROR: The execution of post-install.php has failed with the following message: Execution installer has failed with exit code 9, stdout: Adding user and group plesk-ssh-terminal. stderr: useradd: group plesk-ssh-terminal exists - if you want to add this user to that group, use -g.

Cause

There is already user and group plesk-ssh-terminal leftovers in the server

Resolution

1. Log in to Plesk.

2. Connect to the Plesk server via SSH.

3. Remove the SSH Terminal extension:

   # plesk bin extension --uninstall plesk-ssh-terminal

4. Remove the SSH Terminal group and user leftovers::

   # userdel plesk-ssh-terminal
   # groupdel plesk-ssh-terminal

5. Reinstall the SSH Terminal extension:

   # plesk bin extension --install plesk-ssh-terminal