Apple Pay lets you not only make purchases with the iPhone 6 and iPhone 6 Plus at local retailers that support the service, but also online through many apps, which also supports many more devices. Therefore, it's important to make sure your shipping and billing information is correct so merchants know where to send all the things!
How to update and manage your shipping and billing info for Apple Pay
Launch the Settings app on your iPhone or iPad running iOS 8.1 or later.
Tap on Passbook & Apple Pay.
Tap on either Billing Address or Shipping Address.
Enter any additional addresses you need to, but tap on one address that you'd like to set as a default for each.
That's all there is to it. Apple pay will abide by the settings you've chosen. If you ever need to change your billing or shipping, just repeat the same steps again. This is handy if you have work and home addresses that you choose for shipping equally. It'll save you some time when checking out so you can just select them instead of having to enter information every time.