`contact_change_state_invalid`

HTTP 409conflict

The recipient has already confirmed receipt, or the delivery has ended or gone to paper, so its e-mail address and phone number can no longer be changed. A bounced delivery is sent again as a new delivery.

Handling it

Fix the request and send it again. message says what is wrong, and param names the parameter where there is one. Keep the request_id: it lets Parasend find the request.

The error, as the API returns it

{
  "error": {
    "type": "conflict",
    "code": "contact_change_state_invalid",
    "message": "The recipient has already confirmed receipt, or the delivery has ended or gone to paper, so its e-mail address and phone number can no longer be changed. A bounced delivery is sent again as a new delivery.",
    "param": null,
    "request_id": "req_5e69684dc3de68bf8651a712"
  }
}