Please make sure you have the latest version of attendance installed for the version of Moodle you are using - keep in mind that I do not support Moodle versions that are no longer supported by Moodle.
- what version of Moodle are you using and what version of the attendance plugin do you have installed?
If you are using the QR rotation feature, make sure the time of the machine displaying the QR code is correct and synced and your Moodle server also has the correct time - if it is more than a couple of seconds out, it may be displaying the wrong QR code to users or the server may not be able to validate that the qr code is still valid.
- what version of Moodle are you using and what version of the attendance plugin do you have installed?
If you are using the QR rotation feature, make sure the time of the machine displaying the QR code is correct and synced and your Moodle server also has the correct time - if it is more than a couple of seconds out, it may be displaying the wrong QR code to users or the server may not be able to validate that the qr code is still valid.