Hi Yumi1,
Welcome to the Community. It's essential to correctly record your transactions to keep your books up to date. QuickBooks Online is a great program that gives you the ability to easily track your sales and expenses. I'd be glad to point you in right direction to get the support you need to match or make the overdue amount zero.
To properly record your journal entry, would the overpayment be refunded to the customer or used as a credit? I encourage you to consult an accountant. They'll be able to point you in the right direction to record your journal entry to ensure that your books are balanced. If you don't have an accountant, we can help you locate a ProAdvisor in your local area.
Let me know if you have any questions, I'll be happy to help.
