If your A370 displays Pairing failed during the setup and Flow app says Connection lost, remove the Bluetooth pairing from your mobile device settings and Reset Bluetooth connections from your A370. This is done from the Settings menu, tap the Bluetooth icon. Pair the devices again.
If you’ve disabled Bluetooth in the middle of the first setup, close the Update failed message and sign out of Flow app, or force quit the app, and start again.
If you change your mind and cancel the setup, you need to start the setup again from Flow app by going to Support > Get started with new device or do the setup with USB cable and a computer using Polar FlowSync.
If you experience unexpected behavior in Flow app during setup, first force quit it to see if this helps. If not, uninstall and reinstall the app. Reset your A370 if nothing else works.