I think either. but importantly the bone names of the FBX character need to match the bone names of the animation skeleton. Are you able to test importing them into unreal engine?
I don't know how that's possible as the bones are both the same in Blender when I imported both the Animation FBX and the Character's FBX, and I also Exported them from the same file and have not touched the bone names. Can you show me an error or something?
Ok, From what I see, the problem might be "root_x" not being named "Hip" or "Pelvis" as "Root" is the Root bone for both the character and the Animations rigs, so try renaming "root_x" to "Hip" , "Pelvis" or something else and see if that helps.
I have tried this and there are still a bunch of bones like twist bones etc that are not in the animation skeleton but in the FBS skeleton. Which is why I asked if you could match the skeletons please
I can see if I can remove the extra bones, but from what I'm seeing in Blender the extra bones are also in the Animation files. Which Animation FBX zip are you using?