The event is not currently happening
The times on the event are used to determine if an event is currently happening. See this article under "Specifying Check-In Times" for more details.
This message signals that the device you are using is not authorized as a check-in station. See this article detailing how to authorize a new station.
If the device you are using was previously authorized, check the following:
make sure you are using the same device and browser used to authorize
make sure the browser you are using is no in private browsing or incognito mode
if you recently cleared your cookies or local data, you will need to reauthorize
Event Not Found
Make sure the URL is correct and that the event has not been deleted. You can visit the event within One Church Software and click on the "Launch Check-In" button in the top right.
Alternatively, if the event is currently happening, click on the the "Launch Check-In" at the top of the left panel in One Church Software and select it from the list.