Payment Proofs and Payer Proofs

[GBKS]

We had some conversations at a conference this week about how to prove payments, related to BOLT12. In the real world, we get a receipt and use that when we want to return a product or so. What's the bitcoin native version of that? Some thoughts:

• This could be a good sub-page of the daily spending wallet
• Needs to consider proof that a payment was made, and that the user is the payer
• Should address various kinds of payments (onchain, lightning, ark, etc)
• Should work in-person, in-direct (like email), and other channels
• Are Hallmarks a fit? Have not dug deep, but if wallets implement the same way to present these cryptographic proofs (text and visualization of that text), then I could just show you that visual in my wallet, you would compare to the same visual in your wallet, and we'd be set. An actual data transfer via QR code scan would be more thorough technically, but would also be another interaction.
• Somewhat related, but on the topic of refunds, the question about how to get that address to return funds to, also came up. Maybe worth thinking how closely this is related to the proofs.

I'd like to explore and prototype this in Arké.

[matbalez]

Are you speaking here only of in-person payment confirmation? Or online as well?

I've long thought that we are missing something like LNURL-pay for BOLT12 that would allow an intermediary app to get a callback when a payment is made from a user wallet the app does not control.