Runtime Error on Grouping code

I am working on a project in Excel 2010 that requires me to group values in a generated pivot table. Ultimately, I plan to create a loop that will filter the pivot, dynamically group the results, copy the final table to a new sheet, and then repeat for each item in page filter. I have 99% of the rest of the code figured out, but the section that groups the data keeps kicking out a runtime error. Because the data I am working with is senstive, I have created a hypothetical file and the code is still giving me the runtime error in this simplified file. I feel like it has to be something simple, but I can't find it. Any help is greatly appreciated.

Sub Group()

        Dim pt As PivotTable
        Dim ptField As PivotField
        Dim rPTRange As Range
 
        Set pt = Sheet1.PivotTables("GMPerctTableGen")
        Set ptField = pt.RowFields("GMPerct")
        Set rPTRange = ptField.DataRange.Cells(1, 1)
 
        rPTRange.Group Start:=True, End:=True, by:=0.8

End Sub