Hi, Dominic -
What type of barcode? Linear? 2D? What style/symbology (Code 128, QRCode, UPC-A, etc.)? Are you using a barcode font? If so, which one(s) and from what source? How are you generating the barcodes (using third-party software to create a graphics image or by translating the data to map to code points within a font)? What brand/model of printer are the barcodes being printed on? What is the print resolution?
Most importantly, what is the size (width and height) of the barcode? Each barcode symbology has minimum size & resolution standards that need to be satisfied to ensure the barcode can be successfully scanned. It is also important that there is adequate "quiet zone" (white space) before and after (or around) the barcode to help ensure it can be scanned. The specs also spell out the minimum quiet zone dimensions.
Here is a link to a web site where you can review the specs for a variety of barcode symbologies:
https://www.tec-it.com/en/support/knowbase/barcode-overview/linear/Default.aspx
Best regards, John
