Fatal error: Uncaught Error: Call to undefined function is_main_site() in /home/klient.dhosting.pl/interpages/intr.pl/public_html/wp-includes/update.php:813
Stack trace:
#0 {main}
thrown in /home/klient.dhosting.pl/interpages/intr.pl/public_html/wp-includes/update.php on line 813