Barcode not working

Has anyone had experience getting Knack's barcoding to work? I inserted the CSS code and updated the field_#'s, and it does produce what looks like a barcode. But but I've tried multiple devices and nothing will read it.

I also notice that what is generated in Knack (for example for "1"), does not look like what several online barcode (code39) generators look like. They all have 15 vertical lines, while the Knack one has 20-some.

I'm testing this with some very simple bar codes, 1 ... 123456789 ... and some others. No letters. The ones I generated online all can be read.

Any thought? Thanks!

There are different types of barcodes. Could it be an issue with the format?