curl --request GET \
  --url https://api.courier.com/messages/{message_id}/output \
  --header 'Authorization: Bearer <token>'

{
  "results": [
    {
      "channel": "<string>",
      "channel_id": "<string>",
      "content": {
        "html": "<string>",
        "title": "<string>",
        "body": "<string>",
        "subject": "<string>",
        "text": "<string>",
        "blocks": [
          {
            "type": "<string>",
            "text": "<string>"
          }
        ]
      }
    }
  ]
}