How to recognize a delivery failure through the REST API?

Hi,

One of my documents failed to deliver because of an incorrect e-mail address

But all the API response lists is that the envelope has status “sent”:

{
  "resultSetSize": "3",
  "startPosition": "0",
  "endPosition": "2",
  "totalSetSize": "3",
  "nextUri": "",
  "previousUri": "",
  "envelopes": [
    {
      "status": "sent",
      "...": "..."
    },
    {...}
  ]
}

I would like to recognize an issue like this so I can report it in the module we’ve been building, but have been unable to do so with “listStatusChanges” or “Envelopes:Get”.

Is it not the status?
Am I missing some other field?
Do I need a different request?