Creating Credit Refunds/Invoices
If you'd like to refund a credit balance invoice for a customer, go to Income -> Payments -> Refund Credit. You can search by customer, and the a list of credit balance invoices for the customer will be displayed. You can choose the amount for each invoice to refund.
If you'd like to apply a credit balance invoice against a different invoice for a customer, go to Income -> Payments -> Enter Payments. You can leave the Amount blank or 0. Click Next to see a list of all open invoices. Enter a negative Amount Paid for the amount to be taken from the credit balance invoice, and enter a positive amount for the invoice you'd like to apply the credit against. Click Save when done. This will transfer the credit from one invoice as a payment towards another.
You can create a credit invoice by entering a negative line total for the amount of credit a customer is owed (Income -> Invoices -> New Invoice).
You can also create a credit balance invoice by entering a payment for a customer (Income -> Payments -> Enter Payments) that is more than is due, then click the Create Overpayment checkbox before saving the payment. The excess payment will be applied against a blank invoice creating a credit balance.