Can't figure out vertex painting

Hi. Your mesh is vertex painted with the correct color. It does not morph because it has no proper uv_1
Also, unrelated, but clavicle and breast bones affect the bear a bit in some areas, you should remove them. Another thing that should be removed is uv_2, only heads have that

Anyway, just transfer it from a torso
- expand the rig, make top selectable;
- select the backpack, add Data transfer, choose top as Source object;
- enable Face corner data, choose Nearest face interpolated, then choose uv_1;
- apply
- check how the mesh behaves in-game. If you dont want the bear to be affected by all the morphs in the area, you may select it in 3d view and weld uvs in uv_1