Fatal error: Uncaught Error: Interface "Magento\Framework\Event\ObserverInterface" not found in /home/airtimer/public_html/vendor/magento/module-catalog-rule/Observer/ProcessFrontFinalPriceObserver.php:20 Stack trace: #0 {main} thrown in /home/airtimer/public_html/vendor/magento/module-catalog-rule/Observer/ProcessFrontFinalPriceObserver.php on line 20