try to add horizonal line in chart via vba

Hi :D

I cant get a horizontal line added into a chart via vba. If some one could point me to where my error is in the code that ll be very much appreciated!

There are two series of data:
series 1: Y values for the first series are in column P (header "y1" on the worksheet), x values are the count of those y values.
series 2 (horizontal line): Y value is in A1, the x values are in column Q and are equal to the x values of series 1.
A2 defines the last row ie. the end of the data range for the two series.

here is the workbook test01.xlsm


The code has to be compatible with excel for mac.
Thank you so much in advance!
Sophia

If just wanting a horizontal line at the Y value in A1, maybe:
NB: Not tested on a Mac

   ' Retrieve x-values from column Q for the horizontal line
    Set xValuesQ = wsData.Range("Q2:Q" & lastRow).SpecialCells(xlCellTypeConstants)

    ' Add horizontal line series using x-values from column Q and y-value from A1
    With chartObj.Chart.SeriesCollection.NewSeries
        .xValues = xValuesQ
         ReDim xVal(0 To xValuesQ.Count - 1)
         For i = 0 To UBound(xVal): xVal(i) = wsData.Range("A1").value: Next
        .Values = xVal
        .Border.Color = RGB(255, 0, 0) ' Red color for the horizontal line
        .Name = "Horizontal Line"
    End With

    ' Formatting of chart including axis titles, colors, tick marks, etc.

Thanks!!! It works!