Sumproduct and New Dynamic Array Formula

I believe your problem here is that you are using a SUM operation with an array that you really was to only do a partial sum but excel doesn't know how to sum some of it and spill the rest. In any case you should try using LAMBDA function and in particular the BYROWS() helper function to the LAMBDA(). I'm really unsure what you are doing but something like this might be what you want:
=BYROW($A$5#, LAMBDA(r, SUMIFS(Amount, BankPymtIDColumn, r, Amount, "<> ") ) )
note I used SUMIFS instead of SUMPRODUCT only because I think that is more what you were trying to do. You should be able to use SUMPRODUCT just the same.