Setting "license smart source-interface mgmt0" is not an option?

[NeRFuX]

I'm configuring Smart license on nexus for the first time.
I'm able to set mgmt0 as source interface for everything else (ip http / domain-lookup), but when it comes to configuring the "license smart source-interface", mgmt0 is not an option? 

Is mgmt0 used by default if nothing is specified?

Nexus-9k# license smart source-interface ? 
  ethernet      Ethernet IEEE 802.3z 
  loopback      Loopback interface 
  port-channel  Port Channel interface 
  vni           VNI interface 

Checked on:
N9K-C93180YC-FX3 - vers 10.3(5)
N9K-C9348GC-FX3 - vers 10.4(3)

[NeRFuX]

Extra information -  I have added "license smart vrf management" , so this will maybe automagically set source interface to mgmt0 since this a vrf that can't be removed ?

[navtom]

I would also like to know what is the meaning of this?
I am attempting to set up smart licensing with SSM on-prem. And the Nexus (N9K-C93180YC-FX) just will not communicate with it using its mgmt0 interface.

[Flavio Miranda]

@NeRFuX 

transport http use-vrf management

https://www.cisco.com/c/en/us/td/docs/dcn/nx-os/nexus9000/102x/configuration/system-management/cisco-nexus-9000-series-nx-os-system-management-configuration-guide-102x/m-configuring-smart-call-home-10x.html