I have a Samsung Galaxy Ace 3 and I'm trying to use the Garmin Connect mobile app but it is not working. Are there any known compatibility issues with this which means it won't work properly?
Somehow I doubt that you can update the OS beyond what it is now.
However, if you have BT 4.0, you probably shouldn't give up on it. My phone is 4.4.4 but not on the Garmin approved list but I got it to work.
First question is: Are you trying to pair with the Connect app or your phone. The Connect app is the correct answer. If you are paired to your phone directly, forget the device on the phone's bluetooth and do it again in Connect.
If it still doesn't work, I would suggest calling support.
It wasn't until Andriod 4.3 that BLE support was added to standard Android. Older versions will allow GCM to be installed, but you can't pair a device for syncing - you can only see your data that was synced through a pc/mac.