curl -X GET 'https://api.nuntly.com/messages/imsg_01kabn43yqyxn2bx4ve84mczd3/attachments/iatt_01kabn43yqyxn2bx4ve84mczd3' \
  -H 'Authorization: Bearer apk_xxx'

{
  "data": {
    "id": "<string>",
    "filename": "<string>",
    "contentType": "<string>",
    "size": 123,
    "contentDisposition": "<string>",
    "contentId": "<string>",
    "downloadUrl": "<string>"
  }
}