curl --request GET \
  --url https://api.e-invoice.be/api/documents/{document_id}/attachments/{attachment_id} \
  --header 'Authorization: Bearer <token>'

{
  "file_name": "<string>",
  "id": "<string>",
  "file_type": "application/pdf",
  "file_size": 0,
  "file_url": "<string>"
}