Why NWPath.UnsatisfiedReason always return "notAvailable"

Hi! I am trying to use the NWPathMonitor to check if wifi is on or off. However the NWPath object from the monitor always has unsatisfiedReason property being "notAvailable" regardless whether I turn the wifi off or on (unsatisfiedReason doesn't change even if iPhone is connected to wifi, with NWPath.state satisfied..). Below is the simple code I tried.

Can you help me to find the solution pls?

Thank you!

private var monitor = NWPathMonitor(requiredInterfaceType: .wifi)

init() {
        monitor.pathUpdateHandler = { [weak self] path in

            if #available(iOS 14.2, *) {

                print(path.status)
                print(path.unsatisfiedReason)//always notAvailable

                if path.status == .satisfied {

                    print("Connected to internet")
                    print("Wifi is on")

                } else {

                    print("No connection")

                    if path.unsatisfiedReason == .wifiDenied {

                        print("Wifi is off") // never execute !

                    } else {

                        print("Wifi is on")
                    }
                }
            }
        }
        monitor.start(queue: .global())
    }

    deinit {
        monitor.cancel()
    }