Hi Gunther, That error looks like it's coming from a mismatch between your PHP version and the way the inventory-composer-installer module is handling return types. Specifically, it seems to be expecting a void return type, but the syntax for that wasn't properly handled until PHP 7.1+ — and in some older versions of Magento or composer plugins, that can cause issues. A few things you might want to try: Check your Composer version: Composer 1.10 is quite old and might not work smoothly with Magento 2.4. If possible, try updating to Composer 2.x — but back up everything before doing so, just in case. Check module compatibility: Make sure all your installed Magento modules, especially anything inventory-related, are compatible with your Magento version. You might want to remove and reinstall the magento/inventory-composer-installer package. Temporarily disable the plugin: If you're just trying to get past the install/update, and you’re comfortable editing vendor files (just temporarily), you could comment out or adjust the return type in that Plugin.php file — but this is just a workaround, not a long-term fix. Lastly, double-check that you’re not mixing old module versions from previous Magento upgrades. That’s caught me out before. Let me know how it goes! Best, yasmeen
