Payment rails
Extro doesn’t mint a coin. It quotes one price in dollars and settles it on real value — but on a rail the recipient agrees to take.
One price. The recipient names the rails they accept; the payer settles on one they hold.
A protocol action — registering, reaching a stranger, following someone — has a price denominated in USD. The party being paid advertises which rails they accept, in preference order, inside the 402 Challenge. The payer’s wallet then picks one of those rails it actually holds, converts the USD price to it at pay time, and attaches a signed proof the recipient verifies.
So the payer conforms to the recipient — it can’t settle in whatever it likes. That’s deliberate: it lets a creator insist on rails they can actually use, while still keeping the price itself currency-neutral.
The four rails
Webcash · mined e-cash
Bearer e-cash backed by proof-of-work. Mineable right inside the browser node, settled peer-to-peer, no account required.
Bitcoin Ark · VTXO transfers
Off-chain Bitcoin value over an Ark Service Provider. Fast, cheap transfers that settle back to L1 Bitcoin when you want them to.
Vouchers · issuer-scoped
Tokens redeemable 1:1 against an issuer — typically minted by a keyserver at registration. Acceptance is scoped to the issuer you trust.
RGB · contract assets
Client-side-validated assets and contracts on Bitcoin. Used for content licensing and richer settlement where a smart-contract is warranted.
Why several rails? Resilience and choice. A spammer can’t dodge the toll by avoiding one currency, and recipients aren’t forced onto a single settlement system. Every rail terminates in the same signed-proof interface, so the protocol stays neutral while each party keeps control of what they’ll accept.