Typically this information goes in the "Street address" field, but I see who absence of instructions can be confusing to the user. I don't believe the API should be modified for this, but some UI affordance can be nice. Bruno: What do you think?

From the UX perspective it would most likely be nice to be able to have a custom field. There are a couple issues with that:

· We're designing all of the PR UI to optimize for 1-click behavior. Ideally users will, over time, fill out their details so that they can complete purchases by just hitting pay, or perhaps just changing the shipping address or method. The inclusion of a custom field could make that experience impossible.
· My understanding is that the intent of the PR API definition is to provide all of the basic functionality 80% or so of checkout flows require, and not to be the end-all solution. This allows for simplicity on both the user and developer sides. Unstructured data like this, while valuable, could make things way less straightforward.

Ultimately I'd love to understand how the spec authors feel about this idea.

What would be interesting if there was an option with the address that the user can set as information that they can reuse - so if there address is hard to find, etc, then that could be sent to the merchant by default along with the address. 

If this is a requirement for some merchants it could be a blocker from them implementing the PR, so figuring out an elegant UX solution for them would be key if a custom field breaks the simple flow of PR. 

One idea would be to get merchants to ask for delivery information before hand and let the PR handle payments only. 

Merchants could also ask for the specific questions after payment, no?

They could, but that would feel a little odd, as compared to the standard payment flows of ecom sites, once you give over your payment details, you get a thank you message. Asking for extra info at this point would feel a little broken. 

From spec perspective, this info goes into "Street address". For example,
my default shipping address always includes, "3 Peabody Ter, Apt 123, leave
package at the door if no response" in the street address. That way I can
breeze through checkout every time.

This solution could work, would it be possible to have "notes" text field to encourage users to type that sort of information? Or does that depend on Android? 

This part of the UX doesn't feel completely intuitive but this maybe out of scope for the PR API. 

That would be possible.

Is this something that we could add? Then we could add something in the Payments request UI that asks the user to fill it in if it is necessary? 

Not easily. We would need to make spec changes to enable this, as there's no mechanism right now to put this extra data into. How common are these extra fields? how important are they? We haven't had a request for this yet from a merchant, so I'm hesitant to add the complexity.

Since this is more of a spec change, I think it's best to close this issue here. Mustafa, could you re-file at: https://github.com/w3c/browser-payment-api/issues?

Np filed here: https://github.com/w3c/browser-payment-api/issues/548