Cumul Value within Pivot plus Dimension (horizontal)

[beck_bakytbek]

Hi Folks, i have a following data:

PR, Month, Sales

a, Jan,2

a, Feb,3

b, Jan,2

b, Feb,5

i want to Show the cumul.value : rangesum(above(sum(Sales),0,Rowno())) and it does work great, but if i add the horizontal Dimension in my Pivottable, so then my Expression does not work (please see attached screenshot).

Does anybody have any idea how to solve this issue with one horizontal Dimension within my pivottable.

Thanks a lot

Beck