Hi there, userhuini.

As of now, the option to add a QR code to an invoice is unavailable in QuickBooks. However, we can look for an app that will help you add a QR code to a transaction.

You can visit our Apps page through this link: QuickBooks Applications.

Also, if you want to create a custom template for your invoices, you can check this reference: Customise invoices, estimates, and sales receipts in QuickBooks Online.

I'm just around if ever you need help. Keep safe!