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

fetch('http://{defaultHost}/api/v3/store/collections/{id}', 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/{id} \
  --header 'x-spree-api-key: <api-key>'

{
  "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
}

{
  "error": {
    "code": "record_not_found",
    "message": "Collection not found"
  }
}