Why does the balancing attribute of my data source not appear in the integration mappings?

I am using ARCS (Account Reconciliation Cloud Service) specifically for Transaction Matching. I created a Match Type with two data sources, and during the setup of each data source, ARCS required me to specify a balancing attribute. I chose the transaction amount (Amount) as the balancing attribute, assuming it was the correct field to use.

However, when setting up the integration in Data Exchange to load transactions, the balancing attribute I configured does not appear as an available field in the mapping options. I also checked the target application associated with the data source, and the balancing attribute does not appear there either.