Qt Quick - adding coordinate - Help

[L.J.5]

Guys wondering if anybody could tell me where I am going wrong with this one.

Basically I have a button that when clicked I want to add the next coordinate for a polyline and then for it to show up on my map - however nothing seems to happen.

Any ideas how to add the coordinate and update on map?

Here is the code:

 MapPolyline {

        id: polyline
        line.width: 3
        line.color: 'pink'
        path: [
        { latitude: 53.336272, longitude: -2.837986000001 },
        { latitude: 53.33583666169488, longitude: -2.837948799133301 },
        { latitude: 53.33487728642166, longitude: -2.857099771499634 },
        { latitude: 53.334353, longitude: -2.855717999996 }
              ]
        }

and for the button:

 Button {
        id: button3
        x: 17
        y: 193
        width: 104
        height: 23
        text: qsTr("Test Alpha ")
        onClicked:{
            polyline.addCoordinate(53.33378174636405,-2.8531837463378906)
            update(polyline)
        }

Cheers!