Confirm the application supports the selected PHP release and take a recoverable backup. Record the current PHP version, handler and Apache/nginx proxy settings. Only installed and permitted combinations appear in the customer panel; server-wide installation requires the appropriate administrator.

1. Open the exact domain in Websites & Domains > PHP Settings. Record the current values before editing.
2. Choose a supported PHP version accepted by the application, then inspect the available handler choices. On Linux, PHP-FPM served through Apache and PHP-FPM served through nginx imply different request paths.
3. Check the domain Apache/nginx settings. An application dependent on Apache .htaccess rules needs those rules accounted for before switching to nginx-only processing.
4. Change one variable at a time where possible. Save the handler selection during a maintenance window or first apply it to an equivalent staging site.
5. Test the application and review logs. Also check scheduled commands because their CLI PHP environment can differ from the website request handler.

Test the home page, login, uploads and a database-backed action. Confirm the effective PHP runtime through the panel or an authenticated diagnostic, and remove any temporary public diagnostic file afterward. Compare error rates and resource use with the previous configuration.

If the application fails, restore the recorded handler and version, then investigate the precise error. Missing PHP extensions, incompatible code and ignored Apache rules require different remedies. Do not keep switching randomly or globally replace server PHP to fix one domain.

• Adjusting PHP limits for one Plesk domain
• Finding PHP errors for a Plesk website
• Understanding nginx proxy mode and static files in Plesk
• Creating and downloading a full subscription backup in Plesk

• Plesk: Customer Guide
• Plesk: Choosing The PHP Handler