curl --request GET \
  --url https://api.loopreturns.com/api/v1/collections \
  --header 'X-Authorization: <api-key>'

{
  "collections": [
    {
      "id": 123,
      "external_id": "<string>",
      "channel": "<string>",
      "name": "<string>",
      "products": [
        {
          "id": 2,
          "external_id": "<string>",
          "sku": "<string>",
          "name": "<string>"
        }
      ]
    }
  ]
}