If the barcode scanner scans but the desired items don't appear in the cart, this indicates that the barcode scanner isn't correctly connected to the iPad or iPod via Bluetooth. In this case, try to reconnect the scanner.

If the iPad / iPod keyboard no longer appears because you're using the POS handheld scanner, or if items can't be scanned properly, this could be because the scanner is no longer in iOS mode. Follow the instructions here to put the barcode scanner back into iOS mode.