WooCommerce Event Manager is a great solution for managing events and this is a simple solution for managing QR code for attendee sign in or Checkin on Event spot

QR Code Addon Settings, Admin can assign or allow any user role as QR code or ticket Checker:

After enabling QR code Addon QR code will be added to pdf Ticket:

If user allowed checker Scan Ticket with QRL apps then it will be open like this. as checkin button still in ticket that means this ticket never question and it is valid:

If user allowed checker Scan Ticket with QRL apps then it will be open like this. no checkin button in ticket that means this ticket already used or checkin before and it is in-valid:

Admin Can see report how many attendees passed in the event gate by checking attendee list check-in status.