The best way to not lose your code is to take a screen grab of your ticket code.
QR codes are like barcodes - a graphic representation of a number or alphanumeric string of numbers and letters.
Try webqr.com to read the code, then enter the code manually (without the lowercase letter at the end) at LiveMetallica.com
If you have lost your code or get an invalid code error message when you try to scan, please open a support ticket to request a new code.