PySide6 registering to QScxmlStateMachine event failure - pyside6

Question

PySide on Python 3.10.5
PySide6.__version_info__ = (6, 3, 0, '', '')
Using QScxmlStateMachine connectToEvent(), method I always get the message:
qt.core.qobject.connect: QObject::connect: No such slot ...
The error happens when the slot has an argument of type QScxmlEvent. No error when no argument in the slot but such slot is not useful. The C++ code can use many overriden connectToEvent signatures, PySide only has one of them and it resembles the old signal-slot way, using the SLOT macro.
The code is:
from PySide6.QtWidgets import QApplication, QWidget, QPushButton, QVBoxLayout, QLabel
from PySide6.QtCore import SLOT, Slot, Qt
from PySide6.QtScxml import QScxmlStateMachine, QScxmlEvent
class MainWindow(QWidget):
def __init__(self, scxml_file_name: str) -> None:
super().__init__()
self.machine = QScxmlStateMachine.fromFile(scxml_file_name)
if self.machine.parseErrors():
raise Exception()
self.machine.start()
layout = QVBoxLayout(self)
self.label = QLabel(self)
self.label.setAlignment(Qt.AlignCenter)
layout.addWidget(self.label, 0)
to_local = QPushButton('To Local', self)
to_local.clicked.connect(lambda: self.machine.submitEvent('to_local'))
layout.addWidget(to_local, 0)
to_global = QPushButton('To Global', self)
to_global.clicked.connect(lambda: self.machine.submitEvent('to_global'))
layout.addWidget(to_global, 0)
to_quit = QPushButton('To Out', self)
to_quit.clicked.connect(lambda: self.machine.submitEvent('to_out'))
layout.addWidget(to_quit, 0)
exit = QPushButton('Quit', self)
exit.clicked.connect(self.close)
layout.addWidget(exit, 0)
self.setLayout(layout)
self.machine.connectToEvent('exiting', self, SLOT('on_exiting(QScxmlEvent)'))
self.machine.reachedStableState.connect(lambda: self.label.setText(
', '.join(self.machine.activeStateNames()))
)
#Slot(QScxmlEvent)
def on_exiting(self, event: QScxmlEvent):
print(event)
if __name__ == '__main__':
app = QApplication()
win = MainWindow('statechart.scxml')
win.show()
app.exec()
The statechart is:
<?xml version="1.0" ?>
<scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" name="Statechart" initial="global">
<state id="global">
<transition event="to_local" target="local"/>
</state>
<state id="local">
<transition event="to_global" target="global"/>
<transition event="to_out" target="quit">
<send event="exiting">
<param name="state" expr="local"/>
</send>
</transition>
</state>
<final id="quit" />
</scxml>
I just can't figure out why the connection fails.