How to unbind 'singleclick' event in Openlayers 6 (React)

I want to add a marker on the OpenLayers map with a single-click event. and after adding a marker-> I want to remove this single-click event from the map.

Here is my on-add marker function :

    let iconFeature = new OlFeature({
       geometry: new OlPoint(event.coordinate),
       name: 'Somewhere near Nottingham',
       });
       editLayer.getSource().addFeature(iconFeature);
  };

This is single-click event: map.on('singleclick', onAddMarker);

I tried this way, but not working map.un('singleclick', onAddMarker);