QML charts gridline styling

EqiupmentConnected

I'm using a ChartView with LineSeries and I'd like to make the grid lines dotted or very thin but I can't find anything that tells me how to do it or if it is possible. I tried using gridLinePen but it gives me the error "Unable to assign int to QPen". Can this be done with a QML chart?

ChartView
{
id: line

            anchors.fill: parent
            backgroundColor: "black"
            legend.visible: false

            ValuesAxis
            {
                id: xAxis

                min: -12
                max: 12

                tickCount: 12

                gridLinePen:
                {   style: Qt.DotLine } // does not work

                gridLineColor: "green"
                gridVisible: True
                minorGridVisible: True
            }

            ValuesAxis
            {
                id: yAxis

                min: 0
                max: 70

                tickCount: 40
                gridLineColor: "green"
                gridLinePen: { style: Qt.DotLine }  // does not work
            }

            LineSeries
            {
                id:ls1
                name: "1"

                axisX: xAxis
                axisY: yAxis

                color: "cyan"
                width: 4
            }

            LineSeries
            {
                id:ls2
                name: "1"

                color: "cyan"
                width: 4
            }
        }
    }