QR Code not working properly

I am trying to get the QR code check-in to work. I have successfully set it up to add the QR code to the user emails after they register (image 1). I enabled check-in in the Events Booking configuration. I then logged in to the front end of my site (I have SU access) and then scanned the QR code with my iPhone. I have used several different QR readers including the one tested by the developers. However, I get the following message (image 2). It says it successfully checked in, but it appears to be an error and in reality it doesn't check in, the user never gets a checked in status.

What am I doing wrong?