Error after installing the Simple module in OpenCart 3: Twig_Loader_Array not found

After installing the popular Simple module for simplified registration and checkout in OpenCart 3, some users may encounter an error when updating the modification cache:

 Fatal error: Uncaught Error: Class 'Twig_Loader_Array' not found

Cause of the error

This error is caused by an incompatibility of one of the old modifications installed with the Simple module with newer versions of OсStore.

The culprit is the modification file: /system/simple_twig_fix.ocmod.xml

It is intended for older versions of OpenCart (up to 3.0.2.x), but may conflict with current installations.

How to fix the error

To fix the error, you need to delete or rename the file simple_twig_fix.ocmod.xml so that it is not applied when the modification cache is updated.

1. Navigate to the /system/ directory of your site.
2. Find the file simple_twig_fix.ocmod.xml
3. Delete the file completely or rename it so it won’t be picked up by the system (for example): simple_twig_fix.ocmod.xml-disabled
4. After that, go to the OpenCart admin panel and update the modification cache:
   Go to the Extensions - Modifications section.
   Click the “Refresh” button in the top right corner (blue arrows icon).

After deleting or renaming the file and updating the cache, the error Class 'Twig_Loader_Array' not found should disappear. The Simple module will continue to work correctly, since this modification is no longer needed in modern versions of OcStore, such as OcStore Liveopencart.