Android Studio – Device is connected but ‘offline’

Try these:

• Unplug and replug the USB cable.
• If it still doesn’t work, unplug the USB cable, disable then enable USB debugging in the device settings.
• If the above two methods fail, reboot the device.
• If rebooting the device also fails, reboot Android Studio too.
• If reboot Android Studio still fail, try adb kill-server then adb start-server.