The balance of your customers can be affected by credits and overpayments. Depending on the way credits are issued, they will immediately affect the balance or generate available credits for future orders.
When creating customer credits you'll find the following situations in the customer's balance:
When a customer credit is created and the credit is approved before the payment is posted, the balance of the order will be reduced (only the balance, not the amount of the invoice). The customer will only pay the remaining balance on the order.
When the credit is approved after the payment is posted, the amount of the credit will appear as available credit to be used in the next payment.
If a payment has been applied by using a customer credit and it is cancelled, the open credit will be also cancelled since the payment is no longer valid.
If the customer doesn't have open invoices the system allows you to generate overpayments that will be shown as available credits for future orders.
Available credits can be seen under the Account Receivables >> Receive Payment tab by selecting the customer's name. This information will also appear when creating orders for your customers on the "Customer Information" section.