Historically New Zealand's government has found that compliance isn't massively improved by empty threats, and police resources aren't available to have an officer at the front door of every shop in the country and enforce such a law, so there isn't one.
What does improve compliance is an actual negative event. The change in public reaction to funeral restrictions in lock down when people attending a funeral got sick (and I think one died?) was noticeable. Reported consequences make the policy much harder to ignore. And if there hasn't been enforcement the way human memory works, if on Tuesday a human decides complying with a rule is good, they are now more likely to remember having complied with it on Monday, and retrospectively they will come to believe "obviously" they always obeyed that policy, it was the sensible thing to do.
That's cheaper and more effective than policing. But it may cost a few lives to provide the example.
Compliance could be easily checked by the mystery shopper method though. If a store gets fined for not enforcing QR codes through a random check, they're more likely to enforce it and deny non-scanning shoppers entry.
