Front end capacity license can be confirmed from "Licensed Capacity" "smartdisk license --show" command.
Front end capacity license is the capacity limit when backing up all your clients data.
For example, if you want to backup below 3 servers, you need to a 6TB license and it should be shown in Feature(4) as 6TB .
Server A: 1TB
Server B: 2TB
Server C: 3TB
Only the total size of all clients full backup is counted, not the differential/incremental backups.
This value will be different and lesser than the Total Data Protected in SmartDisk seen in the Web UI which will also count other jobs and duplicates.