Adding a QR code to the invoice can be achieved by integrating with POM, Payconiq, Mollie, or EPC. Once the integration is set up, a QR code will automatically be added to the invoice.

How do I add a QR code? 

To add the QR code, go to the layout and scroll down until you see the 'QR code' option. Then, select your preference (POM, Mollie, EPC) and choose the desired position on the page.

If you choose to work with different QR codes and set them per layout, create multiple templates (layouts) and select the appropriate layout for each invoice.

When you go to the invoice, you will see that the QR code has been successfully added.