Expired transactions

If an attempt is made to commit a transaction which has timed out, you will see the following error:

404 Not Found
Content-Type: application/json

{
    "results": [],
    "errors": [
        {
            "code": "Neo.ClientError.Transaction.TransactionNotFound",
            "message": "Unrecognized transaction id. Transaction may have timed out and been rolled back."
        }
    ]
}