Hi Harald!
No problem I appreciate your response!
I'm using spine-unity-3.8-2019-08-23.unitypackage
I got the files thru git and When I move the files (which are 6) to another folder no error is thown.

If I add those 3 files exported from spine I get no error but this message

As for the preview, this asset has only default skin and several animations, so de default pose the asset is hidden however If I choose an animation I can see it

Thanks a lot for your time!