The prompt that comes up to initiate Apple Pay has a section for the shipping information. If you click that, you can create multiple locations and addresses for each location. You can even create custom emails in the same way under the email section.
Is that what you were doing and were unable to do it or was there some kind of technical issue?
There's a prompt after you hit buy where it requires you to either double-tap the side button (on iOS) or TouchID (on MacOS and some iOS devices). On that prompt, it shows all the transaction information including shipping info, the card Apple Pay will run the transaction on, and the contact information for the transaction.
You must have been speeding through and missed it.
Is that what you were doing and were unable to do it or was there some kind of technical issue?