Hello MrsJenk,
There are two possibilities I see here. I obviously can't know for sure since I'm not ATG or develop for their website. The site either doesn't support this feature anymore (which is the least unlikely since the button is still there). The other option is there was either an update to how Apple handles this functionality and it broke the older buttons OR a recent update to the website broke the button and it has been yet to be updated on the websites end.
Apple isn't responsible for this and it must be implemented by the developer of the website. If the functionality is broken, it is best to reach out to the website and notify them it is no longer working!
I hope this helps!