1. Poor quality of QR code: The QR code is poor in quality, damaged or blurred, and cannot be scanned and identified. You can try to get the QR code again or switch to another QR code for scanning.
2. Insufficient scanning distance: If the distance is too far or the angle is incorrect, the scanning cannot be successful. You can try scanning the QR code at a closer distance or at a more correct angle.
3. Unstable network connection: Unstable network connection or slow network speed will lead to the failure of QR code scanning. You can try to switch to a more stable network environment, or try again when the network is back to normal.