Fatal error: Uncaught Error: Call to undefined function is_main_site() in /var/www/vhosts/awxpokmt.host213.checkdomain.de/htdocs/playground/wordpress/wp-includes/update.php:1080 Stack trace: #0 {main} thrown in /var/www/vhosts/awxpokmt.host213.checkdomain.de/htdocs/playground/wordpress/wp-includes/update.php on line 1080