Sendig UDP packets with specified local port

I am trying to write a UDP client in Swift 5 which sends data to a UDP server which is running on a windows machine. The UDP Server is written in c#

The c# end does this:

IPAddress ipAddress = IPAddress.Parse("192.168.1.228);
IPEndPoint endPoint = new IPEndPoint(ipAddress, 10010);

udpClient = new UdpClient(endPoint);
udpClient.Connect("192.168.1.53, 4001);
udpClient.BeginReceive(new AsyncCallback(ReceiveCallback), null);

And my Swift client is this:

class MeetingMaker {
	
	var connection: NWConnection?
	var host: NWEndpoint.Host = "192.168.1.228"
	var port: NWEndpoint.Port = 10010
	var m2h: MotionToHost = MotionToHost()
	var timer = Timer()
	
	func send(_ payload: Data) {
		connection!.send(content: payload, completion: .contentProcessed({ sendError in
			if let error = sendError {
				print("Unable to process and send the data: \(error)")
			} else {
				print("Data has been sent")
				
			}
		}))
	}
	
	func startSendingUpdates() {
		Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { timer in
			self.sendTick()
						
				}
	}
	
	func sendTick() {
		if connection?.state == .ready {
			//print("MB SEND")
			send(m2h.asData())
		}
	}
	
	func connect() {
		connection = NWConnection(host: host, port: port, using: .udp)
		
		connection!.stateUpdateHandler = { (newState) in
			switch (newState) {
			case .preparing:
				NSLog("MB: Entered state: preparing")
			case .ready:
				NSLog("MB: Entered state: ready")
			case .setup:
				NSLog("MB: Entered state: setup")
			case .cancelled:
				NSLog("MB: Entered state: cancelled")
			case .waiting:
				NSLog("MB: Entered state: waiting")
			case .failed:
				NSLog("MB: Entered state: failed")
			default:
				NSLog("MB: Entered an unknown state")
			}
		}
		
		connection!.viabilityUpdateHandler = { (isViable) in
			if (isViable) {
				NSLog("MB: Connection is viable")
			} else {
				NSLog("MB: Connection is not viable")
			}
		}
		
		connection!.betterPathUpdateHandler = { (betterPathAvailable) in
			if (betterPathAvailable) {
				NSLog("MB: A better path is availble")
			} else {
				NSLog("MB: No better path is available")
			}
		}
		
		connection!.start(queue: .global())
	}
	
}

And elsewhere :

meetingMaker.Connect()

And

meetingMaker.StartSendingUpdates()

The issue is that the UDP Server on windows never receives the packets. I think it expects them to come from source-port 4001? I cannot find how to bind my Swift UDP CLient to send from a specified local port?

(The IP addresses are fixed and correct).

Is it possible to use Swift to send UDP packets from a specific local port, to the specified destination port? Or is the issue elsewhere?