execute : upd-vd-license
Use this command to enter a Virtual Domain (VDOM) license key.
If you have a FortiGate- unit that supports VDOM licenses, you can purchase a license key from Fortinet to increase the maximum number of VDOMs to 25, 50, 100 or 500. By default, FortiGate units support a maximum of 10 VDOMs.
Available on FortiGate models that can be licensed for more than 10 VDOMs.
execute upd-vd-license <license_key>
The license key is a 32-character string supplied by Fortinet. Fortinet requires your unit serial number to generate the license key.