QML does not recognize ENUM returned by C++ Q_INVOKABLE function

[Kofr]

QML

console.log("model's category is " + converter.getModelCategory(currentIndex))

C++

Q_INVOKABLE Unit::Category getModelCategory(int index) { //TODO put in separate file
    qDebug() << "getModelCategory is called, Index is " << index;
    return qobject_cast<Unit *>(CategoryDataModel.at(index))->category();
}

error
: Error: Unknown method return type: Unit::Category where Unit::Category is C++ enums and it is declared with Q_ENUM. However, Unit::Category is declared in other QOBJECT derived class, might it be a problem?
How to solve this issue?

[luosen]

As far as I know, "Unit" type need to register throgh qmlRegisterType to make "Unit::Category" visible in QML.