Bounced Checks

If you want to show that the check was returned and a customer still owes the money, then just enter a Payment with a negative amount (manager or higher access level is usually required for negative payments).

If you want to also cancel the charges (as a write-off) so they don't have a balance due, then you need to first put in the negated charges.  For instance go to Select Rates, add the rates to be negated, and check the "Invert amounts" box to make them negative before clicking Done.  Then, enter a negative Payment (or a Refund) so the balance is $0.

You can also add a Memo transaction to show the reason for the entries, or just change the Description of the Payment or Refund to show something like "NSF" (this is bank language for Insufficient Funds).