1. Due to insufficient light, barcode scanner can't read the bar code correctly.
2. The barcode is defiled, which makes the barcode scanner unable to recognize it correctly.
3. The code scanner is too far away from the bar code to be correctly identified.
4. The code scanner is out of order, resulting in recognition error.
If this happens, you can try to adjust the position, distance and angle of the barcode, or try using another scanner. If you still can't see the barcode clearly, it is recommended to contact relevant departments for repair or replacement.