Apple Pay 'Invalid Shipping Address'

I can see this question has been asked many times, and apparently no-one has been able to give an authoritative answer. Apple Support cannot answer it either.

Using Apple Pay on an iPhone 13 Pro Max (fully up-to-date), no matter which card I attempt to use, trying to make a payment on a website returns the dialogue 'shipping address invalid'. Yet it is exactly the same as the billing address, it is exactly the same as the address the card operators have, which is exactly the same on all cards, and Apple Pay works perfectly at the till. I have tried re-entering the address manually with no success. The only answer is to fill in all the payment forms manually and ignore Apple Pay.

For someone who's been with iPhone since Day 1, this is a deal-breaker. It should not be this difficult, and by now (looking at this forum, the problem is years old) there should be a concise guide to getting it solved. There isn't.