If when you start the app you just see a set of spinning red dots, this indicates that there is a problem getting a location on your phone. Please go to your Settings here:
Settings -> Privacy -> Location Services-> Ensure Turned On - Also, check for "Check-In" in the list of apps and make sure "While Using the App" is selected.
Settings -> Location -> Ensure Turned On - Also, App Permissions -> Supermarket Check-In -> Allow only while using the app
Hopefully that should solve the issue. A new update has just been released (1.0.6+20) which will show the proper messages regarding this rather than leaving you with the spinning red dots of death!