How to sum these volumes, per group?

Question

i am working with spotfire and i need some help. I am trying to sum these volumes for each lot but since i have more than one row for each lot, it is summing all the volumes (which is wrong, i only want to add a single value of volume). How can i do this?

my cross table

I am still new to this, so i am trying to use custom expressions like this: enter image description here

but its resulting this: enter image description here

but since i only have 2 groups, there should be only 2 volumes per group