I think this is a neat idea, but it seems like the UX of it is a bit fraught for two reasons: 1. It doesn't seem like there's any callback mechanism. Once I tr

I think this is a neat idea, but it seems like the UX of it is a bit fraught for two reasons: 1. It doesn't seem like there's any callback mechanism. Once I transfer money, the source has no knowledge of that. If this is used for an invoice, the invoice needs to wait for the transfer to happen on the back-end for the source page to become aware that it happened. There seems to be no possibility of a "thanks for paying" URI that can be triggered after payment. This limits practicality for non-donation payments. 2. Each payto URI represents one payment method. Any payee who wants to accept money in one of a few different payment methods must provide separate URIs. This offloads the burden of knowing _how_ to pay to the user. If there's a list of five payment methods (as five payto URIs), I need to be aware of which ones I have apps for that my user agent can interact with. Some may trigger an error. Versus another world where I click a single link (payto URI) representing five payment methods in one and my user agent asks which app/account/etc I want to pay from.