[ Solved ] Mesh will not import at all.

Hi. For the future, we only need to see the blend file that you tried to import in the package.
You should watch a different tutorial because things are not done right.
- the hair must have 3 meshgroups in the blend: the base shape and two hat chops. They have the same type but different cut numbers. Clone any maxis hair, export the blend and study it;
- the blend must also contain the rig, do not import the hair in the empty blend. Clone something, export the blend, open it, import whatever you need, then adapt it;
- the mesh is not rigged. The vertex groups are in the list but do not affect the mesh;
- the mesh is vertex painted with the wrong color;
- your hair goes below the neckline, you need to transfer the data from something that does as well;
- the uvs do not need to be that small, you can use the whole space meant for hair;
- whatever you were told to do in 2.8+ versions of blender can be done in the compatible version.

The weights, uv_0 and cut numbers are right but a uv_1 and vertex paint are missing. The hair will not morph with the head.
You can transfer uv_1 from head_2. Just make it selectable first.

Vertex paint with 007F02. (the roots are painted with a different color, 007F3F, so you can just transfer vertex paint from a similar hair the same way uv_1 is transferred (just choose VCol instead of UVs))

Yeah, it seems helpful but also was not tailored for what I was trying to do.
Here: