I would think the number just has to be formated with a barcode font. Have you got the barcode font?
However there are many different barcode standards and thus fonts, to name but a few for UCC-12 (UPC-A and UPC-E), EAN-13, EAN-8, ISSN, Bookland and ISBN.
You need to make sure you are using the appropraite font for your needs. You also may need to purchase the font in the first instance.
Regards
DAv
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