I've recently bought a couple Monster cans and they don't work either. I'm from the UK, so the way to redeem the codes seems a bit different (theres a 10 digit code underneath the pull tab, you don't need to photograph the receipt and sent it off to anybody to claim the code. There's also seems to be no access to the snapchat filter). I read this article from Eurogamer claiming that the Halo Infinite Monster drinks won't be available in the UK until October. This got me thinking. Maybe this type of can is only exclusive to UK/Europe? This could explain why the codes don't work; the cans aren't supposed to be shipped out until October, so the codes aren't currently available. This is just my theory.
Here's the article where it came from. I see nobody else confirming UK codes for October, just Eurogamer:
If any 343i members would like to disprove or confirm this, it would be highly appreciated.