Quicksight sumif with calculated fields

Question

I want to find the difference per month of PA test (max({PA amount}, [{ExID}])) and FA test (max({FA amount}, [{ExID}])) but only when both PA test and FA test have values.

So in the below image I want just to have the difference in 62267 and 62258 because these are the only rows that both PA and FA have values. So this works fine.

But when I pull out the appointment from the visual it sums all values per month regardless if there are nulls in PA test or FA

I tried with the below function but nothing happened. Empty result.

sumIf({PA test}, isNotNull({PA test}) AND isNotNull({FA test}))

How can I have the expected result?