Nested Add-ons - Confused

Hi,
New to Xano, sort of have the gist of add-ons. But struggling to the get the sum of a related table. Can I do this in Add-ons, if not then what. Confused.

Client - Loans - Transactions.
1 client many loans. 1 loan Many transactions[image.png]
I can get the count of loans per client. I can get the sum of transactions per loan.
I can't seem to get the sum of transactions per client.

Proposed end result in front end. The outstanding to be a sum of transactions for all of clients loans. [image.png]
Here I am using the numLoans addon to get the count of loans.
[image.png]
The logic is sum all the transactions for all the loans per customer

Any direction would really help.
Much Appreciated.
Graham