{
  "event": "recipient_failed",
  "recipient_id": "255e591c2c9fe1bc99be1ec03075b402",
  "envelope_id": "7e8f68e4c6df9395cd7ff48d69d7e2c1",
  "failed": "2019-12-17T05:30:00Z",
  "method": "email",
  "diagnosis": ""
}
Triggered when an email or SMS delivery attempt to a recipient fails. The payload includes a diagnosis field that contains the raw delivery error returned by the recipient’s mail server or telco provider. You may respond to this event by: 
{
  "event": "recipient_failed",
  "recipient_id": "255e591c2c9fe1bc99be1ec03075b402",
  "envelope_id": "7e8f68e4c6df9395cd7ff48d69d7e2c1",
  "failed": "2019-12-17T05:30:00Z",
  "method": "email",
  "diagnosis": ""
}