Embed gnuplot inside existing QtWidget

I am creating a (pseudo) real-time plotting application in C++, using gnuplot as my backend for plotting. One of my requirements is that the plot must be inside an existing window, instead of having a separate plot window (which gnuplot defaults to).

Gnuplot has an option to specify the (Qt) widget ID which seems like this would fit my use case:

set terminal qt widget <id>

I tried passing the value inside my QtWidget::effectiveWinId() to no avail.

Update: Tried using the internal value of the window id QtWidget::winId() with no luck as well.

The problem is that I cannot find any documentation on what <id> is supposed to be. Is this what the developers of gnuplot intended?

Here's an example of my code:

#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>
#include <QtNetwork/QLocalSocket>

int main()
{
    QApplication app(argc, argv);
    QWidget win(nullptr, Qt::Window);
    QWidget *window = win.window();
    win.show();
    std::cout << "effective win id: " << window->effectiveWinId() << "\n";
    std::cout << "effective win id: " << win.effectiveWinId() << "\n";
    return app.exec();
}

In gnuplot:

gnuplot> set term qt widget <value from effectiveWinId>
gnuplot> plot x
Could not connect to existing qt widget. Starting a new one.