Hey Ruben,
Thank you for reaching out to us! If you are trying to scan the QR code using an android device, can you please make sure that it is logged into your WordPress site with sufficient permissions to handle your tickets? To be able to scan QR codes at your events, you must be logged into your site.
If you are already logged in and the issue persists, please let us know and we will be happy to assist!
Also, this article might be useful if you want to know more about QR Codes and how they work.
I hope this helps! Let me know if you need anything else in the mean time!
Regards,
Patricia