It is never fun when your big event comes, and your scans are failing.
1) The first thing to check, is on your Ticket Types, (My Ticket Space > Ticket Types) to see if you have incorrectly set the check-in date or time allowed. This is likely the case, and is preventing them from being scanned in, which is by design, because you don't want other ticket types for another event, to be used.
2) If that does not solve your issues, ensure that your check-in app is using the correct API Key under My TIcket Space > Settings > API Access. It could be that your app has auto-logged in under the wrong API key for your event.
3) Check to see if the ticket has already been checked in. Maybe a ticket was accidentally (or purposfully?) printed twice and is trying to be used. You can check
4) If you are still having troubles, check your timezone for your ticket space, to ensure that your timezone is set correctly. You can check your timezone under Adv Site Settings > General. It is recommended to select a City nearest to you, because that way any daylight savings time will automatically adjust. If you select an offset number instead of a city, you may need to adjust when daylight savings time comes.
5) Hopefully this is not the case, but ensure that the ticket you are scanning is a valid ticket. The whole point of the check-in apps are to validate that the ticket is real, and that it has not been checked in past the allowed number of times.
If you still experience troubles, please contact us and let us know.