What this procedure is
How to enable debug mode when you cannot access the Back Office by editing a configuration file.
Applies to: PrestaShop 8.x.
Why you would do this
- See the real error on screen.
- Diagnose a 500 error or blank page.
Prerequisites
- FTP/File Manager access.
- Access to store files.
Quick diagnosis (before you change anything)
1) Locate the defines file
Expected result: find config/defines.inc.php.
Enable debug without Back Office (defines file)
Step 1) Edit the file
Open config/defines.inc.php and set _PS_MODE_DEV_ to true.
Expected result: after reload you will see the real error.
Step 2) Reproduce the issue
Open the failing page to capture the message.
Step 3) Disable debug after diagnosis
Set _PS_MODE_DEV_ back to false in production.
Final verification
- You see a specific error (not generic).
If something doesn’t work (common issues)
Nothing changes
- Confirm you edited the correct file.
- Clear cache manually.
Best practices
- Do not leave debug enabled in production.
- Share the error with support if needed.