Hair Mesh Won't Import

Hi. The link leads to this thread, need to click on Create link when adding it

The reason the mesh wont import is the absence of cut numbers

The file should be structured differently for this to happen successfully
Unrelated to the problem at hand, but certain things should be done differently for the hair to work properly

Start by studying a similar ( has an accessory) hair ( things that are wrong or missing in your blend are in cursive)
- clone yfHair_EF09BraidWovenFlowers, export the blend, open it. You will see three meshgroups: a base shape of the hair and two hat chops. Each of them has different cut numbers, which is how s4s knows what 3d model in the blend should replace what in the package;
- you will also notice that the accessory is joined with the hair mesh, that is how it should be. The uvs and textures of this accessory are in the hair area in uv_0;
- if you were to look through other components of either meshgroups, you'd see that they have two uv maps: uv_0 defines how textures are displayed, uv_1 defines how the hair will morph in-game;
- hair should be vertex painted, otherwise it will not morph correctly. This type of data can be transferred from the reference
- you should also never transform the item in Object mode;

Recreate:
- open the blend with your hair, join the accessory with the hair, export it as obj with Selection only enabled( this will remove all unnecessary data);

- clone yfHair_MediumStraightParted, export the blend open, delete hat chops, rename the remaining mesh to Reference;
- import your hair;
- enable proportional editing and move the strands at the back a bit away from the neck;

- select the reference, shift-select the hair, transfer weights with these settings, then use Clean tool with All groups and Limit total;

- create a new uv map. Rename the first one to uv_0, the second to uv_1 ( no caps);
- add data transfer, choose Reference as source object, set the rest like in the pic, apply;

- transfer vertex paint the same way

- choose uv_0, move the uvs of the hair band into the area meant for hair;
- delete the reference, duplicate your hair twice, give them cuts 0000, 0001, 0002;

- save, import into yfHair_MediumStraightParted package

S4Studio_Mesh_1 Is Rinnehair_mesh. The provided images are just examples of what to click, prioritize the text.
Your hair is the receiver of data, so everything should be done to it, not the reference or anything else.

In object mode, select the hair, the press shift + D + enter. Do this two times in total. You will then have three identical meshes. Ideally, two of the meshes should be altered by you to make hat chops, of course, and all three should be given different cut numbers. Even if you choose not to make hat chops you should have three meshes with three separate cut numbers. 

Share the updated blend and package files please

The uv_1 is not correct and the mesh is not vertex painted, so it wont morph.

Either re-download the blend file you shared in the first post and follow the instructions without skipping steps or watch a video tutorial on converting hair to ts4 to familiarize yourself with the process in a better format.