Fatal Error after Activation


i try to install Support system Plugin to s single wp site and get this error after activation:

Fatal error: Call to undefined function get_current_site() in /var/www/vhosts/domain.com/knowledgebase/wp-content/plugins/incsub-support/incsub-support.php on line 259

Is it only for wp multisite and cant be used on a single wp installation?