Turn Sumproduct Calculation Into vba

Try this

Sub t()
Dim lr As Long
 lr = Worksheets("Download").Cells(Rows.Count, "i").End(xlUp).Row
 Range("G4").Resize(Cells(Rows.Count, "h").End(xlUp).Row) _
    .Value = "=SUMPRODUCT((Download!$I$4:$I$" & lr & "=""CUSTOMER1"")*(Download!$H$4:$H" & lr & "=CUSTOMER1!H4)*(Download!$G$4:$G$" & lr & "))"

End Sub