Pack overlay not working

what is up my dudes
my overlay doesnt work and it is making me very sadge```json
{
    "pack": {
      "pack_format": 18,
      "supported_formats": {
        "min_inclusive": 18,
        "max_inclusive": 27
      },
      "description": [
        "boop"
      ]
    },
    "overlays": {
      "entries": [
        {
          "formats": [26,27],
          "directory": "new_grass"
        }
      ]
    }
  }
it still uses the old, non-overlayed file, and i cant figure out what im doin wrong