Hi, I really need your help!

I have a set of data with X and Y values.
From the set I create a scatter plot.
I now would like to write a VBA to do the following.

The user should click on a point in the scatter plot.
After that the user clicks on a bottom which triggers the VBA.
The VBA should extract the X and Y coordinate of the point in the chart and write it to a cell.
Can you help me with that?

I already have the following code, but it doesn't work?
Sub GetCoordinates()
    Dim IDNum As Long, a As Long, b As Long, arrX, arrY, X_Wert, Y_Wert
    Dim x As Long
    Dim y As Long
    Dim sc As Series
    ActiveChart.GetChartElement x, y, IDNum, a, b
    If IDNum = 28 Then
         MsgBox "gut"
        Set sc = ActiveChart.SeriesCollection(a)
        arrX = sc.XValues
        arrY = sc.Values
        X_Wert = arrX(b)
        Y_Wert = arrY(b)
        ThisWorkbook.Sheets("Sheet1").Range("C1").Value = valueX
        MsgBox "Please click on a series in the chart."
    End If
End Sub

Thanks a lot!