Hi, @Balloonhead.

At this time, we can only set up an automatic reminder message in QuickBooks Online. You'll need to manually send the reminders when their invoices are or soon to be overdue.

To set up automatic invoice reminders message, please follow the steps below:

1. Go to the Gear icon⚙ in the right corner.
2. Select Account and Settings under Company Settings.
3. Click the Sales tab.
4. In the Reminders section select Edit ✏️.
5. Click the box beside Auto invoice reminders.
6. Select the due date for unpaid invoices in the drop-down arrow.
7. Choose a greeting from the dropdowns.
8. Edit the subject and email message. You can also stick with the default message.
9. Tick the box beside Email me a copy at noreply@quickbooks.com. So you'll get a copy of the email that your customer's invoices are or soon to be overdue.
10. Select Save and then Done.

Once you've done, you can follow the steps provided by my colleague AlcaeusF on how to send reminders in the system.

Also, I'm adding our Income and expenses page. It provides topics that might help you navigate your QuickBooks account.

Let me know if you have additional questions or concerns. We're always around here to guide you. Be safe.