MODBUS custom command doesn't work

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QObject *connector = new QObject();

    QModbusTcpClient *client = new QModbusTcpClient();
    client->setConnectionParameter(QModbusDevice::NetworkAddressParameter, "127.0.0.1");
    client->setConnectionParameter(QModbusDevice::NetworkPortParameter, 8899);
    client->connectDevice();

    QModbusResponse::registerDataSizeCalculator(QModbusPdu::CustomFun_ReadData, [](const QModbusResponse &)-> int
    {
        qInfo() << "Custom data size calculator"; // this line wasn't printed out
        return 42;
    });

    connector->connect(client, &QModbusClient::stateChanged, connector, [connector, client]()
    {
        if(client->state() == QModbusClient::ConnectedState)
        {
            auto cmd = QModbusPdu::FunctionCode(QModbusPdu::CustomFun_ReadData);
            QModbusRequest request(cmd);
            qInfo() << "Is request valid? " << request.isValid(); // true
            QModbusReply* reply = client->sendRawRequest(request, 1);
            qInfo() << "Reply is null: " << (reply == nullptr); // false
            qInfo() << "Is response valid? " << reply->rawResult().isValid(); // false, we didn't get it yet
 
            connector->connect(reply, &QModbusReply::finished, connector, [reply]()
            {
                qInfo() << "isFinished? " << reply->isFinished(); // true
                qInfo() << "Is response valid? " << reply->rawResult().isValid(); // false, even though reply finished
                qInfo() << "Raw result fun code: " << reply->rawResult().functionCode(); // 0
                qInfo() << "Error? " << reply->errorString(); // ""
                qInfo() << "Reply data size: " << reply->rawResult().dataSize(); // 0
                qInfo() << "Reply size: " << reply->rawResult().data().size(); // 0
                QByteArray data = reply->rawResult().data(); // ""
            });
        }
    });

    return a.exec();
}

QModbusResponse::registerDataSizeCalculator(QModbusPdu::CustomFun_ReadData ...

QModbusResponse::registerDataSizeCalculator(QModbusPdu::WriteSingleCoil ...