The Loyverse app has 2 different scanners: A QR code scanner, and a barcode scanner. First of all I just want to make sure that you are using the right one.
Assuming that you are using the right scanning option, try the next thing.
At the Loyverse app, in your item card, check that the barcode is correct (it may have an extra cero). Try to delete it, and then add again the barcode by scanning with the built in camera.
If you keep having problems you should approach the customer support team and send some images, or better, a video, to explain in detail the situation: how you added the barcode to the item, how you are scanning the item, etc. they will be happy to listen to you.