curl --request GET \
  --url https://api.courier.com/notifications/{id}/content \
  --header 'Authorization: Bearer <token>'

{
  "blocks": [
    {
      "alias": "<string>",
      "context": "<string>",
      "id": "<string>",
      "type": "action",
      "content": "<string>",
      "locales": {},
      "checksum": "<string>"
    }
  ],
  "channels": [
    {
      "id": "<string>",
      "type": "<string>",
      "content": {
        "subject": "<string>",
        "title": "<string>"
      },
      "locales": {},
      "checksum": "<string>"
    }
  ],
  "checksum": "<string>"
}