Which statement is true about using credit memos in QuickBooks Online?

Using credit memos in QuickBooks Online provides a mechanism for adjusting customer balances when a return is made or if there was an overcharge. The correct statement reflects that a credit memo can be directly applied to an invoice for the specific customer it was created for. This is a key function of credit memos, as it allows the business to decrease the customer's outstanding balance efficiently, acknowledging any goods returned or services not delivered satisfactorily.

This functionality facilitates a seamless return process, ensuring accurate accounting and providing customers with proper credit toward future purchases. By linking the credit memo to an invoice, it maintains clear records of transactions and helps in reconciling accounts.

The other statements do not accurately represent how credit memos work within QuickBooks Online. For example, credit memos are not restricted to invoices from just the past month, and they can be used for more than just cash refunds, but rather as a way to adjust accounts for customer transactions. Lastly, credit memos indeed have a default application to invoices and are designed to be used in conjunction to manage customer accounts effectively.