This check-in mode uses the location abilities of a phone to verify a person's presence at check-in time.
Such location abilities rely on GPS, Wifi signals, and cell-tower locations, which are most reliable
outside. So, your group should really have a clear view of the sky when they check-in.
We have a dedicated
inside check-in method
here.
You can try using the map-based method for indoor check-ins (many of our customers do!), but likely 5-10% of your group will not be able to check-in. Their phones will report "too far away."
It all depends on the type of building you're in and what may be around you, so be prepared to do some manual check-ins.