Depending on the barcode type, only an even number of digits may be possible:
With type 2, you can only store article numbers with an even number of digits correctly in the barcode, e.g. 6-digit or 8-digit numbers.
Type 1 allows odd and even number of characters, i.e. 12-digit and 13-digit EAN. However, with this type the barcode will be very narrow and may not be suitable for every scanner.