I have a situation where I am trying to create a summary values for the Users list and have them be arranged by a 'type' mapping.
I have a mapping module dimensioned by users and my 'product' list, with a list formatted line item to determine if it is applicable to them and what type it is for them, and I was hoping to use a SUM formula to bring it together - see mock up:

However, when I set the formula Source.Values[SUM:Map.Value to User by Type] I get the error: "Dimension of mapping used for aggregation doesn't match any dimension of the source" which seems wrong, since the mapping has the 'Product' list, which matches the source just fine.
So then I created an additional intermediary line item where the original values line item is just directly referenced in a module that has the dimensions 'Products, Users', then when I tried I got the error: "Invalid use of 'Users' list with function 'SUM'" ...
I checked the 'Constraints' section of the 'SUM' function on Anapedia, and see no reference to the User dimension, so what is actually happening here? Why is it invalid?
It seems like the first error message is misleading, and the second error message is the actual root cause, unless I'm missing something? And if it is indeed invalid and I'm not just missing something silly, what would be the workaround for this goal?