mesh parts do not come together

I’ve been creating hair for a while, I’ve noticed that several hair creators use only two mesh in the blender, one for the mass of the hair without transparency and a mesh for the transparency of the mesh, I tried to do this technique by joining mesh 2 with mesh 1 in the sims studio to be perfect but inside the game it doesn't work


testing within the game I saw that when I add a hat the transparent part is apparent and the non-transparent part disappears

thanks in advance...