Joomla errors after a PHP upgrade: a safe troubleshooting order

Confirm what changed

A runtime change can expose incompatibilities in extensions, templates, or custom libraries that previously worked.

1. Write down the old and new PHP versions if the host provides them.
2. Capture the visible error and affected URLs without exposing secrets publicly.
3. Check the Joomla version and installed extension support status.

Use controlled diagnostics

The safest place to reproduce the failure is a staging copy with equivalent PHP and extensions.

1. Preserve a copy of site files and the database before changing production versions.
2. Review available PHP and Joomla logs instead of displaying detailed errors to public visitors.
3. Test extension and template compatibility systematically.

Decide between repair and migration

Short-term stabilization is appropriate only when security and hosting constraints permit. Some sites need replacement extensions or a staged migration to supported Joomla.

1. Identify blockers and dependencies.
2. Plan a testable cutover and rollback path.
3. Verify authentication, forms, content routes and business-critical functionality after any change.

Relevant official documentation

These references inform the general guidance. They do not verify any individual site's condition.

Need someone to investigate?

You can describe the symptoms without identifying the cause yourself. Credentials are not requested in the public form.