In this documentation, we can check how to enable maintenance mode in PHP-Fusion.
1) Login to PHP-Fusion admin panel.
2) Go to the tab ‘System Admin’.
3) Click the icon ‘Security’.
4) Go to the section ‘Maintenance’.
5) Select the maintenance level.
6) Enable the maintenance mode and type the maintenance message.
7) Click the button ‘Save Settings’.
That is how we can enable maintenance mode in PHP-Fusion.