Same method i mentionned above, but just after generating the random code or link or whatever use the QR Code component to create a QR code for it and after getting the link either insert it as image in your email body HTML code or as attachement, of course send the email using eFeMail extension and don’t forget to enable isHtml parameter if you’ll use HTML codes. And to scan it with the app use Barcode Scanner component (it scans both barcodes and QR codes).