How to fix autoload error, Manual installation vs Magento composer installation

Autoload errors can occur when the same module or a shared package is installed twice using different methods (Composer vs. manual).

When this happens

• Installing a WeltPixel extension via Magento Marketplace (Composer) (under vendor/weltpixel) and updating the same extension manually (under app/code/WeltPixel) causes an autoload error because the module is defined twice.

• Installing one WeltPixel extension via Marketplace (Composer) and a second one manually via weltpixel.com can also cause conflicts when both rely on a shared dependency (e.g., the “Backend” dependency pack) that ends up in two locations:
• app/code/WeltPixel/Backend
• vendor/weltpixel/m2-weltpixel-backend

Solution

Remove the duplicate so that only one copy remains installed:

1) Keep Composer install; remove manual copy

• Delete the manual version under: app/code/WeltPixel/<ExtensionName>

2) Keep manual install; remove Composer copy

• Remove the Composer version under: vendor/weltpixel/<extensionname>

After removing the duplicate, run your typical maintenance commands (e.g., php bin/magento setup:upgrade, recompile, deploy static content, and clear caches) to finalize the fix.

How to uninstall (manual vs. Composer)

For detailed uninstall instructions for both methods, see:

How to uninstall and remove a Magento 2 extension (manual vs composer)

Updated on: 16/09/2025