Hosted addresses and the pay-by-the-call proxy4

Public addresses, with no key: the id in the address is the credential, as it is on a hosted checkout page. A checkout session's and a payment link's share_url send a browser on to the hosted page and answer a client that asks for JSON (Accept: application/json, or the address ending .json) with a description it can act on. /pay/{resource_id} fronts a priced resource: 402 until paid, then the request is forwarded to the address the business registered. Errors are { error: { code, message } }, or the paying protocol's own on a 402.