How can I use inter process communication?

Hi, I am currently building my own VPN application using NetworkExtension's PacketTunnelProvider.

I want to send information from the PacketTunnelProvider to the ViewController when a VPN connection fails and to tell the user why.

The code now is as shown below. When the startTunnel() being overwritten is executed, somehow NotificationCenter.default.post(name: NSNotification.Name.NEVPNStatusDidChange, object: nil) is executed and VPNStatusDidChange(_ notification: Notification?) in the ViewController is called and displays some message.

I tried to do the same thing by writing NotificationCenter.default.post(name: NSNotification.Name(rawValue: "testnotify"), object: nil) in the PacketTunnelProvider.swift , but it does not work. What is wrong?

Here is a part of current PacketTunnelProvider.swift

override func startTunnel(options: [String : NSObject]? = nil, completionHandler: @escaping (Error?) -> Void) {

  conf = (self.protocolConfiguration as! NETunnelProviderProtocol).providerConfiguration! as [String : AnyObject]
  self.setupWSSession()
   
  DispatchQueue.global().async {
    while (self.connectionPhase < 5) {
      Thread.sleep(forTimeInterval: 0.5)
    }
    self.tunToWS()
  }
  NotificationCenter.default.post(name: NSNotification.Name(rawValue: "testnotify"), object: nil)
}

And here is a part of ViewController.swift

override func viewDidLoad() {
    super.viewDidLoad()
    initVPNTunnelProviderManager()
    NotificationCenter.default.addObserver(self, selector: #selector(ViewController.VPNStatusDidChange(_:)), name: NSNotification.Name.NEVPNStatusDidChange, object: nil)
    
    NotificationCenter.default.addObserver(self, selector: #selector(ViewController.receieve(_:)), name: NSNotification.Name(rawValue: "testnotify"), object: nil)
   
}


@objc func VPNStatusDidChange(_ notification: Notification?) {
  print("VPN Status changed:")
  let status = self.vpnManager.connection.status
  switch status {
  case .connecting:
    print("Connecting...")
    connectButton.setTitle("Disconnect", for: .normal)
    break
  case .connected:
    print("Connected...")
    connectButton.setTitle("Disconnect", for: .normal)
    break
  case .disconnecting:
    print("Disconnecting...")
    break
  case .disconnected:
    print("Disconnected...")
    connectButton.setTitle("Connect", for: .normal)
    break
  case .invalid:
    print("Invliad")
    break
  case .reasserting:
    print("Reasserting...")
    break
  }
}


@objc func receive(_ notification: Notification?)  {
    print("receive Notification!")
}