Good evening and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the issues you have encountered with our QR checkin functionality.
I would love to help you with this topic.
As a first step, I would recommend reading the following: https://theeventscalendar.com/knowledgebase/using-qr-codes-event-tickets-plus/
Secondly, can you confirm that you have logged-in to your site’s wp-admin section prior to scanning the ticket ?
Hang in there!
Geoff B.