To get background notifications, you must authorize the application "Always" access to your location.
In the top left of the beacons list, tap the "Info" button and tap the "Application Settings" row. This will take you to the settings page for the Leash app where you can change your location access preferences. Make sure that location is set to "Always".
If you no longer want to receive notification, you can uncheck the "Background Notifications" setting on the Edit Beacon page inside the Leash app.