...
The tab is used to record the bank charges applied to this outgoing payment to the customer. To record the bank charges, you need to select the Apply Bank Charges check box on this tab—this makes the appropriate fields available.
The "Bank Payment (create)" form. The Bank Charges tab
...
In the Expense Item field, specify an expense item intended for bank expenses.
In the Business Activity field, specify a business activity for such expenses.
...