I appreciate you joining the thread, @cmeisel.

I'm here to share some workaround for adding additional reminders or notes within your invoice receipt in QuickBooks Online.

We can add new terms for the invoices. I'll teach you how:

1. Open and invoice
2. Go to the Terms dropdown arrow.
3. Then select Add New. From there, you can specify Monthly, Quarterly, or Annually to your invoice.
4. Add the number of days and hit Save.

I added screenshot for you reference:

Another workaround is to include a reminder on our invoices by adding the Message on the Invoice box. This way, you'll be able to communicate to your customer clearly and effectively. 

Additionally, here's an article you can refer to about enhancing an invoice into an eye-catching one: Customizing Invoices Within QuickBooks Online.

I'll be there for more queries about your sales forms and other reports you need to pull up. Let me know in the comment section. Have a great day ahead.