private gateway - vxlan support?

[bradh352]

My guest network is all vxlan:

I try to create a private gateway using this and a vxlan outside this range (inside the range also doesn't work):

But it uses vlan:

Of course the vlan id is outside the range that vlans support.

And I can see in the VR no new NIC is created since obviously this is invalid:

If I try to use vxlan://4100 instead, it tells me doing that is invalid:

So does that mean I must use VLANs?