How 402 works
HTTP reserved a status code for “payment required” and the web never used it. The Extro 402 scheme picks it up — as a signed, in-band handshake between two nodes, not a web response.
The handshake
When someone who isn’t your friend tries to reach you, your node doesn’t just accept the message. It answers with a signed challenge and waits for payment.
- 1
Challenge
recipient signs the price + rails it accepts
- 2
Pay
sender settles on an accepted rail it holds
- 3
Retry
payer attaches the signed proof
- ✓
Delivered
the message reaches the inbox
Mutual follows skip this entirely — friends are always free.
- Challenge. The recipient’s node returns a signed payment required message: the price, the rails it will accept (in preference order), a single-use nonce, and who to pay. Signing it prevents anyone forging a toll in your name.
- Pay — on a rail they accept. The sender’s wallet picks one of the advertised rails it actually holds and settles the inbound fee. The payer conforms to what the recipient accepts; it can’t just pay in whatever it likes.
- Retry. The sender re-sends, now carrying a signed payment proof bound to that nonce.
- Deliver. The proof checks out, the message lands.
The Challenge and Retry travel in-band over the WebRTC data channel as compact signed binary messages — not as HTTP responses. The Extro 402 scheme is a protocol idea, not a web request.
Why it stops spam
Spam is a volume business. It only works when reach is free. The moment every unsolicited message carries a real, non-refundable cost, the entire economic model of spam inverts — and the payment doesn’t go to a platform, it goes to the person being reached.
Friends are free
The toll only applies to strangers. If you and someone both follow each other, you’re friends — and friends message each other for nothing. The fee is purely a gate on unsolicited inbound reach.
Bidirectional pricing. Each person sets their own inbound price. A transfer’s cost is the difference between the sender’s outbound price and the recipient’s inbound price; mutual follows force that delta to zero. A daily-spend cap bounds how much anyone can subsidize reaching strangers.
Beyond the base handshake. The same signed-402 idea composes into a family of reusable schemes — encrypted bearer delivery, exact-fill order requests, ARK 2-of-2 release/refund, proof attachments, and seeder publish fees. See Extro-402 schemes for the wire-level detail. And note this economy applies identically to peers and agents alike.