Agent Pays for an API

The companion proof for s402 — not the protocol, but an agent actually using it. An autonomous agent calls a paywalled API, gets back 402 Payment Required, reads a price it never knew, signs a Sui payment, retries, and receives the data. No API keys. No human in the loop.

What happens

1. Agent calls a free endpoint → data, no payment.
2. Agent calls a premium endpoint → 402 + machine-readable s402 terms (exact, amount, asset, payTo). It discovers the price.
3. The agent's s402 client signs a Sui transaction and retries with an X-PAYMENT header.
4. The server settles on Sui testnet and returns 200 + data + a receipt carrying the on-chain tx digest.

The server holds no key — it only broadcasts the agent's signed transaction. Trustless by construction.

Run it

pnpm install --ignore-workspace
export SUI_TESTNET_PRIVATE_KEY=…   # a funded testnet wallet
pnpm exec tsx demo.ts

Demo

Terminal recording lands here — every premium response is backed by a real Sui testnet transaction, with Suiscan links printed in the run.

Proof

• npm: s402 — the protocol, published and installable today.
• Built on @sweefi/sui.
• Verified: server + 402 handshake observed live; full settlement issues real testnet transactions.