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

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

{
  "data": [
    {
      "id": "prod_UkLWZg9DAJ",
      "name": "Product 2516979",
      "slug": "product-2516979",
      "meta_title": null,
      "meta_description": null,
      "meta_keywords": null,
      "variant_count": 1,
      "available_on": null,
      "preorder_ships_at": null,
      "purchasable": true,
      "preorder": false,
      "in_stock": false,
      "backorderable": true,
      "available": true,
      "description": "Accusantium ex dicta error nemo ipsa vel eaque porro. Laborum ipsam molestias iure aspernatur quos dolorem. Quia libero odio nesciunt debitis eaque.",
      "description_html": "Accusantium ex dicta error nemo ipsa vel eaque porro. Laborum ipsam molestias iure aspernatur quos dolorem. Quia libero odio nesciunt debitis eaque.",
      "default_variant_id": "variant_UkLWZg9DAJ",
      "buy_box_variant_id": "variant_UkLWZg9DAJ",
      "thumbnail_url": null,
      "tags": [],
      "price": {
        "id": "price_UkLWZg9DAJ",
        "amount": "19.99",
        "amount_in_cents": 1999,
        "compare_at_amount": null,
        "compare_at_amount_in_cents": null,
        "currency": "USD",
        "display_amount": "$19.99",
        "display_compare_at_amount": null,
        "price_list_id": null
      },
      "original_price": null,
      "seller_id": null
    }
  ],
  "meta": {
    "page": 1,
    "limit": 25,
    "count": 1,
    "pages": 1,
    "from": 1,
    "to": 1,
    "in": 1,
    "previous": null,
    "next": null
  }
}