There are two reasons why the pre-registration code is not recognized on the display:

1. The visit date is incorrect or does not match the current date
   When a QR code has been sent to a visitor it will only be active during the day(s) that have been configured. For example, a visitor who arrives a day early and tries to scan the QR code will get an error while doing so.
   
   
2. The checkbox 'I have a QR code' is not ticked in the visitor display profile
   In order to scan the QR code the checkbox, 'I have a QR code' must be ticked. This can be found within the Visitor Display Profile. More can be found in the article below:

Create or modify the visitor registration display profile