Who is it’s? Apple Pay may share the address you have as the default address at this path,
iPhone > Settings > Wallet & Apple Pay > Apple Pay Defaults > Shipping Address >????
Generally your Wallet shares the address associated with your payment method. Click on the card and the billing addresses you’ve entered are shown.
The merchant sometimes confirms addresses with the bank. If they don’t match what the bank has on record, the merchant will decline. Also if you have an account or prior purchases with the merchant, they may cross reference card information with their account records. Again a mismatch will decline the transaction.