Can a recurring invoice be scheduled for every three years, or is yearly the longest option?

Looks as though yearly is the longest option. 

Hi there, @accounting582. Let me provide some details about setting up a recurring invoice in QuickBooks Online.

Currently, the option to create recurring invoices every three years is unavailable in QBO. The longest you can go is a year, Just me is right. Other than that, only Daily, Weekly, and Monthly are available.

In the meantime, I recommend you provide us with your thoughts by sending feedback about this. Your helpful recommendations will be gratefully included by our product developers to enhance your QBO experience. To do so, follow these steps:

1. Open the Gear icon, then select Feedback.
2. Fill in your comments or product suggestions. 
3. Once done, click on Next to submit feedback.

Feel free to browse the QuickBooks Online Feature Requests webpage to review any recently update ideas.

I'm also adding these helpful articles you can read about handling recurring transactions:

• Create recurring transactions in QuickBooks Online
• Recurring transaction doesn't send automatically

You can always get back to use in case you need more help regarding this or QuickBooks in particular. We're here to back you up 24/7/ Take the best care!