Ah, yeah. Zip code is used for credit/debit card verification by many, many online or otherwise card-not-present transactions. It must match, or it gets rejected at an early level. Bank or card company doesn’t usually see such early rejections. Framework probably doesn’t see it either. Similar as if you entered your CVV, card security code, wrong. Credit/debit cards don’t seem to use the +4 zip. So I think you should always leave it off the billing address at minium.