Retainer refunds are recorded as system-generated vendor bills and are not paid using the Bill Payments workflow. As a result, they are treated as miscellaneous transactions in Accounts Payable reports.
If retainer refunds are not appearing in the AP Aging report, verify that Show Miscellaneous Transactions is selected under Display Options. When this option is enabled, retainer refund transactions are included in the report. Alternatively, you can use the AP Aging with Credits report, which includes retainer refund transactions by default and provides additional visibility into credits and related Accounts Payable activity.