Thanks for getting in touch and sorry to hear you're having trouble connecting your reader.
You're actually going to need to get in touch with our support team on 1800 531 738 for further assistance with this. Generally speaking, a mobile device will give you a "Rooted Device" error either if the device is rooted or Square is otherwise detecting a non-secure enough operating environment for card payment processing.
Occasionally there can be issues connecting otherwise supported devices to Square due to the nature of the Android install on the device or the presence of any apps that have altered the Android OS in such a way that it no longer meets our security requirements for processing payments on Android.
One thing you can check is to see if there are any pending security updates available to the OS.