The most common reason for device pairing issues is that there is a mismatch between the app version on your device and the app version that you are trying to pair. Check the console for an app version mismatch notification.
Most QR code readers work with the Insert QR code.
To verify that you don't have a QR reader issue, we recommend to try alternative pairing methods such as sending yourself an email with a pairing link and opening it on your device. If this method works for pairing, try installing a different QR reader for future pairing.