You would need one licence for each device you want to run Xibo for Android on.
If you are no longer using XfA on your old device, you can unlicence it in Customer Portal (after removing the software from it), and then re-use the licence on your new device. You can’t however licence two devices with one licence.
There’s full details of the licencing model here:
If you require support for your licencing, then please email support@springsignage.com directly, and they will be able to assist you.