There are several possible reasons.
1) The function of reading such a barcode is not turned on.
2) The bar code does not conform to the specification, for example, the necessary blank area is missing, the contrast of the bar and the space is too low, and the width ratio of the bar and the space is not suitable.
3) Direct sunlight, the photosensitive device enters the saturation zone.
4) The surface of the barcode is covered with a transparent material, and the degree of reflection is too high. Although the eye can see the barcode, the collector has strict reading conditions and cannot be read.
5) Hardware failure, contact your dealer for repair.