We recently added QR codes to groups and meetings to enable contactless check-in.
We realised COVID-19 requirements mean you need a way for people to also checkout. All you need to do to activate this is enable "Record check in & check out times" on your check-in meetings.
After that change, people who are checked-in can scan the QR code as they leave, and because it remembers the phone number or email address entered for check-in, they only need to tap "Search" and then "Leave" to checkout.