PrestaShop fix 500 error on website

A 500 Internal Server Error in PrestaShop usually means something went wrong on the server, often due to PHP issues, file permission errors, or faulty module/theme code. Here’s a step-by-step guide to identify and fix the issue:

✅ Step 1: Enable Debug Mode

This will show you the actual error instead of a generic 500 message.

Option A: From the Admin Panel

If the back office is accessible:

1. Go to Advanced Parameters > Performance
2. Enable Debug Mode

Option B: Manually via defines.inc.php

If back office is not accessible:

1. Open /config/defines.inc.php
2. Find this line:

   define('_PS_MODE_DEV_', false);
   

3. Change it to:

   define('_PS_MODE_DEV_', true);
   

Then refresh your website and note the error message.

✅ Step 2: Common Causes and Fixes

🔸 1. Broken or Incompatible Module

If the error appeared after installing/updating a module:

• Use FTP or File Manager
• Go to /modules/ and rename the suspected module folder to something like module_name_backup
• Reload the site

🔸 2. PHP Version Conflict

PrestaShop 1.7+ is compatible with PHP 7.1–7.4 (1.7.8.x supports up to PHP 7.4)
Make sure your server uses the correct PHP version. You can check it in hosting panel or ask your host.

🔸 3. File Permission Issues

• Use FTP to check file permissions:
  • Files: 644
  • Folders: 755
• Incorrect permissions may cause a 500 error.

🔸 4. Corrupt .htaccess File

• Rename the .htaccess file to .htaccess_old
• Try to regenerate it:
  • Back office > SEO & URLs > Save (if accessible)
  • Or delete it and regenerate by visiting front office and back office if they load.

🔸 5. Memory Limit or Execution Timeout

Check your hosting’s PHP error logs for memory exhaustion:

• If so, increase memory:

// In config/defines.inc.php
@ini_set('memory_limit', '512M');

✅ Step 3: Check Server Error Logs

• Use cPanel or ask your hosting provider
• Look for the latest log in error_log or /var/log/apache2/error.log

✅ Step 4: Restore from Backup (if necessary)

If nothing helps and the error happened after a major change (theme/module/edit), consider restoring a backup of your:

• Database
• PrestaShop files

🛠 Optional: Reinstall Core Files (Advanced)

If system files are corrupted:

1. Download the same PrestaShop version from official site
2. Upload and replace /classes, /controllers, /override, /src, /tools, /vendor, etc.
3. Keep /img, /upload, /themes, /modules, /config, and /translations untouched.