Mode U requires exactly 19 characters. Extra characters are discarded and short data is right-padded with zeros — the barcode scans, and the human-readable line beneath it is wrong.
Supply exactly 19 characters.
^XA^BY3^FO50,50^BCN,100,Y,N,N,U^FD12345^FS^XZ
^BC in mode U with field data that is not exactly 19 characters.
Neither ^PW nor ^LL is set. Both fall back to a value stored in the individual printer, not to a value in the spec — so the same ZPL prints differently on two printers of the same model.
Set ^PW and ^LL explicitly in every format.
The bar width is outside the GS1-128 range (0.495 mm to 0.940 mm, 0.495 mm target). At 203 dpi that means ^BY 4 or greater.
Raise ^BY to at least 4 at 203 dpi, or 6 at 300 dpi.
At 203 dpi ^BY2 — the power-up default — and ^BY3 both fail GS1.
This GS1-128 is shorter than the 31.75 mm GS1 requires. It may scan on a handheld and fail at a fixed scanner.
Set the height to at least 254 dots at 203 dpi, or 375 at 300 dpi.
Mode U requires exactly 19 characters. Extra characters are discarded and short data is right-padded with zeros — the barcode scans, and the human-readable line beneath it is wrong.
Supply exactly 19 characters.
Silent data corruption that still scans.
This GS1-128 is missing the leading FNC1. Without it the symbol is a plain Code 128 and the scanner will not read the AIs.
Add FNC1 (>8) immediately after the subset start code, or use ^BC mode D.
Silent data corruption that still scans.