Welcome to the Community, lgonsiewski. Currently, automated late fees are unavailable in QuickBooks Online International. As a workaround, you can manually create and add a late fee service item to your invoices.
To do this, go to the Gear icon > Products and Services > New product/service > Service. In the Name field, enter "Late Payment Fee" and add a fixed value in the Sales price/rate box. Once done, click Save and Close.
After creating the item, open your invoice and add it to charge your customer. You will then have this item ready to use whenever you'll need to charge your customer for late payment.
To track these charges later, I recommend running a Sales by Product/Service Detail report. This will show you the total amount billed and which customers were charged.
If you have more questions, feel free to ask. We're here to help.
