I managed to snatch another edit that didn't had the original tail, and made the avatar with no problems. But thanks anyway, your guide will be useful for me another time or for someone else!

If all of this sounds too complicated and you'd rather use my edit, go into the console in unity and take a screenshot. I can probably tell you the issue from there.

I got the edit so I could use the body since the original has a tail glued to its mesh and your edit doesn't.. I was trying to make an avatar for my friend, but trying to upload it to VRChat gives the "clearing blueprint ID" error, I think you might know what it is. And no.. the avatar's prefab doesn't have an ID, I don't know why it happens.

I don't have experience with Blender and when I tried to remove the tail from the original model by myself I screwed up. Do you have any tips on how I can solve this or maybe you have the body without the tail so I could use it? Thanks a lot anyway.