Fatal error: Uncaught Error: Class "Composer\Installers\Installer" not found in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/oomphinc/composer-installers-extender/src/Installers/Installer.php:11 Stack trace: #0 {main} thrown in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/oomphinc/composer-installers-extender/src/Installers/Installer.php on line 11