Invalid property name 'x' (M16)

whenever I set a property.
And nothing is displayed when I launch the app.

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    qmlRegisterType(QUrl("qrc:/MyTimer.qml"), "MyTimers", 1, 0, "MyTimer");

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

main.qml

import QtQuick
import QtQuick.Window
import QtMultimedia
import QtQuick.Controls
import QtQuick.Layouts
import MyTimers

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Timers")
    color: "#000000"

        MyTimer {
            id: timer1
            countdownValue: 30
        }

}

MyTimer.qml

import QtQuick
import QtQuick.Controls

Item {
    id: root
    property int countdownValue: 30

	Rectangle {
		anchors.fill: parent
		color: "red"
                width: 600
                height: width
	}
}

Since it wasn't working I changed the class to have only a rectangle (that it is not shown when I run it).

MyTimer.qml and main.qml are specified in resources.qrc.