Adding a network interface to a Big-IP VE?

I have a Big-IP running v14.1.4.6 and need to add another network interface. At the moment, interfaces 1.1, 1.2 and 1.3 are configured, but I see no option in the GUI to add a fourth. According to the server team folks there's a fourth network adapter configured (in VMware, I believe), but I'm at a loss regarding how to create a fourth one on the F5. I did find the command below (modified for what I need) for adding an interface in another post, but was unable to get it to work.

tmsh create net vlan vlan103 interfaces add { 1.4 { untagged } }

Am I going about this the wrong way? It's odd that adding an interface can't simply be done via the GUI.

Thanks!