I'd like to share a few details in regards to your concern.
Currently, we're unable to add a snapscan QR code to your invoice in QuickBooks Online. We can look for a third-party application that helps QuickBooks to include your QR code in the invoice. Since this option unavailable, I would suggest visiting our blog website so you'll be updated on the new features added in QuickBooks and find out the enhanced features.
Let me know if you have other questions. I'm always here to help. Take care and stay safe.