WooCommerce Event Manager is a great solution for managing events and this is a simple solution for managing QR codes 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 the QR code Addon QR code will be added to the pdf Ticket:

If the user allows the checker to Scan the Ticket with QRL apps then it will be open like this. as check-in button still in a ticket that means this ticket never questioned and it is valid:
If the user allows the checker Scan Ticket with QRL apps then it will be open like this. no check-in button in ticket means this ticket has already been used or check-in before and it is invalid:
Admin Can see how many attendees passed in the event gate by checking the attendee list check-in status.
To Learn More details please watch this video:
You can buy this addon from this URL: WooCommerce Event QR Code Addon