Ambiguous use of observe firebase DB

Question

I really cannot get what is wrong?
I'm trying to load some settings data from firebase Settings node. Same code for other nodes in other functions work but this one is ambiguous. Why?

var ref:FIRDatabaseReference!  //Global variable

     override func viewDidLoad() {
        super.viewDidLoad()


        self.mapView.delegate = self

            if CLLocationManager.locationServicesEnabled() {

                locationManager.delegate = self
                locationManager.desiredAccuracy = kCLLocationAccuracyBest
                locationManager.requestWhenInUseAuthorization()
                locationManager.startUpdatingLocation()

              //  monitorRegion()

            } else {

                // Alert to enable location services on iphone first
            }

            ref = FIRDatabase.database().reference(fromURL: "https://*******.firebaseio.com/")
            //The error is here
            ref.child("Settings").child("service_types").observe(.value) { (snapshot) in

            }


        // Do any additional setup after loading the view.
    }

Answer 1

Change this:

ref.child("Settings").child("service_types").observe(.value) { (snapshot) in

}

to this:

ref.child("Settings").child("service_types").observe(.value, with: { snapshot in

})

See also firebase documentation section Listen for value events