We have been having an issue in which certain rogue items or products that are linked in linnworks.net to our Wordpress, ebay and amazon sites and have a barcode attributed, but are not being recognised by that barcode when scanning out on the linnworks epos program.
I have tested the barcode scanner by even going into linnlive on our till point and double checking the barcode number, and then even scanning it into the barcode section for that product via the scanner. And it is still not recognising them after that.
Are you scanning barcodes from a stock item label? Sometimes barcode can be printed partially where some part of it is cut off. This can happen to long barcodes. Please make sure that barcode is correctly printed.
You can try to scan it to somewhere else, e.g. Notepad. If you can scan it correctly into Notepad, then you will be able to do this in EPOS as well.