Threaded plugs follow “Cartridge Valve” assembly rules.
In this section user is supposed to select
Top Face = non relevant here but you must select (select external plug face)
Bottom Face = mating plane, surface that will match cavity STEP0 plane
Axis = plug axis (thread cylinder axis)
It’s possible to select any planar face from 3d model instead of planes. In case face is not planar, you can create plane with cad commands and select them instead.
If plug is assembled bottom-up, flip bottom face plane normal by using dedicated commands in Inventor or SolidWorks.