In fact that is very simple! :)

The volume must be without internal faces!!!

This follow is the general case who always works! The Bridge function between 2 separated faces!

In this specific case the Extrude will also works because faces are not on the "extremities"
and not touch between them !
Box on the left don't work because Top/ Bottom face are too complex for the Plugin!
You must split it first! With any method but without internal faces! Here there is a new building :)
Use of the SsPlit function is of course used!





Here following Subdivision after Extrude will not work!
Because there are no more "triming faces"!