Browsing contexts don't have an "origin"

[bzbarsky]

https://w3c.github.io/browser-payment-api/#constructor is talking about "a nested browsing context whose origin is different from the top-level browsing context's origin", but browsing contexts do not have an origin attached to them per se. They can contain things that have origins, of course.

I suspect what you want is an "allowed to make payment requests" flag on Document or Window and make sure it gets set correctly in the HTML spec.