Licensing for N-able Backup is different than other N-able N-central features, such as Netpath, where each device consumes a license.
The licensing for N-able Backup is controlled on the backup server, not through N-able Backup. When you add a device, it adds a license, when you remove one is removes the license N-able checks for licenses that have been active that month for billing purposes.
There is no limit to the number of devices in N-able N-central where N-able Backup can be enabled. N-able Backup information does not appear in the Administrative License Usage Report in the N-able N-central.
To determine how many devices have N-able Backup enabled, at the SO level:
Click Views > All devices.
In the Filter drop-down menu, select N-able Backup Devices.
This will display a list of all devices that have N-able Backup enabled.