The auto population of late fees on past due invoices stopped. I followed the tips to make sure nothing changed; they still do not populate. What else could cause this?

Welcome to the Community space, @kcwdbooks.

Let me share info about automatic late fees for past-due invoices and direct you to the best possible help.

QuickBooks automatically adds late fees to overdue invoices for up to six months. You can read this article for more info: Apply late fees to overdue invoices automatically in QuickBooks Online.

If the invoices are not more than six months and the late fees aren't automatically applied, we can manually apply it as a line item by adding it to the Products & services.

Also, I recommend contacting QuickBooks Online (QBO) support to review your account and look for the root cause of why your late fees stopped applying to your past-due invoices. Then, find a solution. 

Here's how: 

1. Sign in to your QuickBooks Online company.
2. Select Help (?).
3. Select either tab to get started:
   • Assistant: Get quick, personalized answers. Select a suggested option, or type a question or topic you need help with. If you decide you need further help, you can still Talk to a human.
   • Search: Search the QuickBooks Online knowledge base directly, or select Contact Us and choose a way to connect with us:
     • Start a chat with a support expert.
     • Get a callback from the next available expert.

You might want to learn how to automatically or manually send invoice reminders. Check out this article: Send invoice reminders automatically or manually in QuickBooks Online.

For additional questions about managing your invoices, click the Reply button below. I'll be willing to lend a hand. Keep safe and have a good day.