If you are using blender the scaling is different for roblox so you have to resize it under the scale option to around 0.1/0.01. I’m not sure why it’s invisible though.
First make sure you’re importing from Blender at the correct scale… check this post solution for reference:
Secondly, make sure all your bones of the rig are within the mesh and you don’t have any overlapping or extra IK bones included that are usually part of the tutorials, that are out there. That was my mistake. Once I took out a couple extra bones that Blender wanted in there for its own animation purposes, I was able to get Studio to import the rigged mesh, perfectly.
Also, make sure you export from Blender as FBX, in case you weren’t aware…