You can navigate to your accounts and settings to enable automatic late payment fees for your invoices, @codiek1. I'll guide you through the steps below.
In QuickBooks Online (QBO), the late fees feature charges fees on overdue invoices to encourage timely payments. Please note that QuickBooks will only calculate and apply late fees to overdue invoices after you enable this setting. You'll need to manually apply late fees as a line item on older invoices.
To enable this feature, follow these steps:
- Go to Settings and select Account and settings.
- Select the Sales tab, and click Edit ✎ in the Late fees section.
- Turn on the Default charge applied to overdue invoices switch.
- Enter the Amount and/or Percent (%) of the fee.
- Choose the Frequency dropdown, then pick how often you charge customers.
- If you want to give them a grace period, select how many days to give them from the dropdown.
- Select Save.

Please see this article for steps to customize late fees for each customer and more information on managing this feature: Apply late fees to overdue invoices automatically in QuickBooks Online.
Furthermore, you can add an account summary to your invoices, allowing your customers to be reminded of their balances. Here’s a detailed article on this process: Add an account summary to an invoice in QuickBooks Online.
If you have any other questions about automatically adding late payment fees in QBO, kindly reply to this thread. It's our priority to ensure everything is taken care of. Have a great day ahead!