Every version of Onthos is only tested against, and only supports, a specific range of PHP and Joomla versions, as published on its download page. These version limits are actively enforced by the software itself, not just documented. This is part of our compliance with the European Union Cyber Resilience Act (EU CRA): we can only vouch for the security of our software, and honour our security risk assessment, within the specific PHP and Joomla versions it was designed for.
If the site you are using is running a PHP or Joomla version outside the range supported by your installed version of Onthos, opening the component in the backend will display a clear error message telling you whether you need to upgrade PHP, upgrade Joomla, or upgrade (or, rarely, downgrade) Onthos itself, and which versions are supported.
The fix is always one of upgrading PHP, upgrading Joomla, or installing a version of Onthos whose supported range matches your server's PHP and Joomla versions — consult our Compatibility page to find a compatible combination.