in the CLI this requires three steps
a) create vlans, e.g. "vlan 1234", "vlan 1235"
b) create a vlan-name,e.g. "vlan-name test"
c) bind the two, e.g. "vlan test 1234-1235"
the API requires the same,
1) call "vlan_id" in Interfaces section
2) call "vlan_name" in L2/L3 Protocols
3) bind them with "vlan_name_id" in L2/L3 Protocols
Warning: do not accidentally choose the API shown default assignment method of "even", choose "hash" (which is the default of the CLI).