const options = {method: 'GET', headers: {'x-spree-api-key': '<api-key>'}};

fetch('http://{defaultHost}/api/v3/store/collections', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

curl --request GET \
  --url http://{defaultHost}/api/v3/store/collections \
  --header 'x-spree-api-key: <api-key>'

{
  "data": [
    {
      "id": "coll_UkLWZg9DAJ",
      "name": "Summer Sale",
      "permalink": "summer-sale",
      "position": 1,
      "sort_order": "manual",
      "meta_title": null,
      "meta_description": null,
      "meta_keywords": null,
      "products_count": 1,
      "description": "",
      "description_html": "",
      "image_url": null,
      "square_image_url": null
    }
  ],
  "meta": {
    "page": 1,
    "limit": 25,
    "count": 1,
    "pages": 1,
    "from": 1,
    "to": 1,
    "in": 1,
    "previous": null,
    "next": null
  }
}

{
  "error": {
    "code": "invalid_token",
    "message": "Valid API key required"
  }
}