Adding X1 Interface (VM)

I'm trying to add in an X1 interface on a newly stood-up SPP appliance, and I'm not sure how to get the X1 to show up.

The appliance has been stood up in vCenter, and it has been given two NICs. However, I'm only seeing X0 when looking at Appliance Management > Networking. What needs to be done to add in the X1 interface? 

Looking in the documentation, all it says on X1 one is what fields you can modify within it, but not what needs to be done to set it up in the first place.