Hello @kautzy1,
Yes, I did a while ago. 
You can read about it in the Faq section - User Tutorials / How To’s.
This tutorial allows you to add a QR code in your pdf template file.
https://community2.invoiceplane.com/t/topic/9877
I just finished another QR code implementation that allows your customers to view their invoice via a public link (e.g. sent via email) AND there via a button to view the QR code in a modal window (and of course pay directly)…
Here’s a screenshot to give you an impression of what this looks like.
