When you set a matter status to ‘Closed’, the default behavior is for the system to run through a series of checks to ensure that certain conditions are met. The matter must not have any pending charges (unbilled time and expense), the case balance must be $0 AND the trust balance must be reconciled to $0 as well. If you do not want to reconcile the matter before closing, this check and default behavior can be turned off via the Settings->Account Configuration area by unchecking the option "Require matter balance to be reconciled to $0 for closure".
You may need to do either of the actions below to reconcile a matter.
If there is a positive balance in the client's trust, and there are no additional charges to be billed on the matter, then you will need to issue a refund.
If there are no funds available in the client's trust, and there is some amount of money outstanding (i.e. owed to the firm), and the client is likely not to pay the balance, you may need to issue a credit in the amount owed in order to balance the matter to $0. Issuing a credit is the preferred method as it leaves a record of the balance that was owned and unpaid, should the client seek additional services in the future. This approach also does not require any change to the contract amount or any of the records and so the integrity of the matter and work that was done is preserved for future reference.