Send a private product attribute

private-attribute.json

{
  "data": {
    (...)
    "attributes": [
      {
        "label": "Important notice",
        "slug": "product-note",
        "visible": 1,
        "taxonomy": false,
        "options": [
          "german"
        ]
      }
      (...)
    ],
  },
  "shop": "demo-shop"
}