So are you saying you cant import Fbx,objs to create new characters?
If so how else are you supposed to create more characters other than purchasing from the marketplace?
The standard way to create custom characters in Character Creator 3 is using morph sliders. You have a number of morph sliders that come with CC3 plus you can add further morph sliders by purchasing add-on packs such as the latest Ultimate Morphs
pack which has everything you need to create unlimited characters.
Alternatively, you can send the CC3 Base character to 3rd party software like ZBrush where you can sculpt the mesh to create your own custom characters/morphs and then return it back to Character Creator.