Because it’s entered incorrectly at one of the four locations it needs to be entered. If a mismatch is detected an error message is generated.
The location that many people ignore is the >> ME << card in the Apple Contacts app on your devices. Make sure the address is correctly entered and labeled properly.
Each card also has an address associated with the account. Please follow this path;
iPhone > Settings > Apple Account (Your Name at top of screen) > Payment & Shipping > tap card to edit > tap Billing address > tap edit (upper right corner of screen) edit necessary changes
iPhone > Settings > Apple Account (Your Name at top of screen) > Payment & Shipping > Shipping Address (edit or delete address)
iPhone > Settings > Wallet & Apple Pay > Transaction Defaults (scroll down) > Shipping Address > Edit (upper right corner of screen) > either Enter New Shipping Address, add new address or edit/delete addresses
There are also AutoFill settings for Safari and your ME contacts card in the Apple Contact app needs to be ordered and labeled correctly. You can create custom labels too if you don’t want to delete old addresses.
Your account with the merchant may also need to be updated as address confirmation are a form of verification and used for fraud detection.