A user cannot check into a site. The app says there is a tag mis-match where the tag has been correctly allocated.
This is just based on the distance the users tries to scan from especially in low light situation. The iOS App returns this error because it reads the QR Incorrectly.
Place the phone's camera approximately 5-10 cm away from the tag.
Attempt to check-in
Slowly move the camera away from the tag slowly.
Stop once you get to 20 cm away from the tag. If you're still not checked-in, repeat steps 1 - 3.
This error is usually resolved once your team works out the perfect distance for their particular phone, camera, device and operating system.