Illustrator/Indesign Overprint for generated EAN barcode is not working

The question has been answered, I think, in a strictly technical manner. However, I'd suggest that SVG is not the best format to use in the first place, and that these problems and many others might be avoidable by exporting to a more standard/ized format like PDF.

SVG keeps rising in usage and it seems to me it's as cranky and problematic as all the other "let's do it different now" formats that have come and gone.

Just for my own interest, is the opening poster the printer at the printing company; or designing a product that will then go to a printing company for production?

I only ask because when preparing labels or cartons, we will often recreate the client's barcode purely because the client does not know what barcode width reduction (BWR) is required for our presses. Here's a TL:DR definition of BWR: https://boxshot.com/barcode/tutorials/bar-width-reduction/

Many of my employer's clients organise a barcode audit with the likes of GS1, and while failures can be rare (and often don't affect the scanability of a code) it can be enough for a supplier to have their product rejected by a retailer, so it is something we take quite seriously.

Sorry, I did not read carfully enough, Brad’s post is right.

I'm going to go on the assumption you changed the file in Illustrator to CMYK, changed your blacks to 100K only, then set overprint, and saved the file as an .ai file. That being said, I found the issue:

The text has an Isolate Blending mode assigned to it for some reason. It doesn't show immediately if you open the .svg file, because the text is grouped, even though it's only one piece of point text, but once you ungroup it, you can see that "Other Options" has been assigned to it in the Appearance panel. Click on "Opacity" and that will bring up the next panel. Uncheck Isolate Blending and resave... you should be good after that.

(also: you might want to outline your text anyway to avoid font issues, even though it's "just Arial"

Hi @default08l4ikj40xtn , SVG is an RGB format, when you open the SVG into Illustrator make sure the Document Color Mode is set to CMYK and the barcode fill is set to 0|0|0|100 black only CMYK. An RGB black would convert to 4-color and there would be no overprint: