reference to connect is ambiguous QQuickItem QMainWindow QCustomPlot

[TheIndependentAquarius]

I am trying to use QCustomPlot's example of the following folder, in my program:

/examples/plots

and at the same time I want it accessible from QML. So, I added <QQuickItem> and it resulted in the error stated in the title.

The code:

#include <QQuickItem>
#include <QMainWindow>
#include <QTimer>
#include "../../qcustomplot.h" 
 
namespace Ui {
class MainWindow;
}
 
class MainWindow :  public QQuickItem, public QMainWindow
{
  Q_OBJECT

#include <QQuickItem>
#include <QMainWindow>
#include <QTimer>
#include "../../qcustomplot.h" 

namespace Ui {
class MainWindow;
}

class MainWindow :  public QQuickItem, public QMainWindow
{
  Q_OBJECT

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What should I do to make it accessible from QML and solve the error too?