@evan Would it be possible to have the payment request and payment receipt as part "in band"? Would it even make sense to do it?
In a not-so-distant past I was working on a project with cryptocurrency to remove onboarding UX problems and make payments easier between people. The project didn't go anywhere because no cares about crypto as actual currency, but it did teach me enough about payment networks that I thought about expanding to support for SEPA (in the EU), Pix (Brazil) and FedNow.