Excel on Mac

Im trying to setup my friends computer to invoice

I have run time 1004 error occurring.

Any help please



Sub NextInvoice()
Range("I13").Value = Range("I13") + 1
Range("B12:E15").ClearContents
Range("B17:E18").ClearContents
Range("B23:G37").ClearContents
End Sub

Sub SaveInvoiceAsPDF()

'Copy Invoice to a new file
NewFN = "Macintosh HD/Users/ambermclean/Documents/DANCE/Dance Teaching Invoices/inv" & Range("i13").Value & ".pdf"
ActiveSheet.ExportAsFixedFormat Type:=xlTypePDF, FileName:=NewFN, _
Quality:=xlQualityStandard, IncludeDocProperties:=True, _
IgnorePrintAreas:=False, OpenAfterPublish:=False
NextInvoice

End Sub