You should be able to see your licensed devices details in Customer Portal -> Android licencing page, when you click the ‘View’ button - Android Licences Management
If you have more licences than devices, then you should be able to licence new devices as well.
There could be version mismatch (if you don’t have upgrades available for example) or an date&time issue on your android devices if there are licencing issues - Licencing your Xibo for Android Display
If there is a specific problem with your licence pool / android devices, please do email Spring Signage support directly with your licence pool email address and we will take a look.