Always mention the check-in date with your messages to avoid confusion.
When I see "Someone already responded to this check-in request" I need to know for sure that it refers to today.
AdminSteve Channon (CEO, Palcheck) commented
That's not a bad idea - I will add it to the list. We are in the process of simplifying things, but it's slow going. For this, as a workaround until it can be the way you describe, I might just update the message to say "Make sure you are responding to the correct current check-in; you may log in online to see if you have a check-in that currently needs a response"