`delivery_state_invalid`

HTTP 409conflict

This delivery has been confirmed or has ended; its follow-ups no longer change.

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": "delivery_state_invalid",
    "message": "This delivery has been confirmed or has ended; its follow-ups no longer change.",
    "param": null,
    "request_id": "req_5e69684dc3de68bf8651a712"
  }
}