One signature. Paid on Robinhood Chain.

For builders

Two sides, one protocol. A merchant mounts the paywall and a payer wraps fetch. Both take a few lines: paywall.ts for the merchant, client.ts for the payer. Keys come from the merchant page.

Get paid

// Hono. Price in USDG; the handler runs only after the payment verified.
app.get('/quote', paywall({ price: '0.01', payTo: '0xYourAddress' }), (c) => c.json(quote()))

Pay

// viem wallet + account. Refuses anything priced above the cap.
const pay = payingFetch(wallet, account, { maxUsdg: '0.05' })
const res = await pay('https://api.metamuse.lol/rh777/demo/quote')
const receipt = decode(res.headers.get('PAYMENT-RESPONSE'))

Prove a receipt later

// The attestation is an rh777 signature over the receipt hash.
await verifyMessage({ address: rail.signer, message: { raw: receiptHash(receipt) }, signature: receipt.attestation })

• GET /rh777/supportedwhat the rail settles, and the signer address behind attestations
• POST /rh777/verifyread only: would this payment settle right now, and why not
• POST /rh777/settlesettles, once per payer nonce; needs a merchant key for the payTo
• GET /rh777/receipt/:payer/:noncethe stored receipt and its hash
• GET /rh777/healthrelayer gas, chain height, settlements so far
• GET /rh777/demo/quote0.01 USDG for a live META quote; try the whole loop in a minute

How it works, plainly

The price is a header. A server that wants USDG answers a normal request with status 402 and a base64 JSON challenge in PAYMENT-REQUIRED. It lists the network (eip155:4663), the asset (USDG), the amount in base units, the merchant address, and how long the offer stands.

The payment is a signature, not a transaction. The payer signs a Permit2 transfer for exactly that amount, with the merchant written into the message as a witness. The spender in that message is a small proxy contract whose only job is to hand the funds to that address. Nobody can redirect it, not even the rail.

The rail pays the gas. rh777 checks the signature, the allowance, the balance, the nonce, the deadline, and simulates the settlement before spending anything. Then it sends one transaction on Robinhood Chain and waits for the receipt. On the demo loop that took 1,251 ms from the first request to the paid answer.

The receipt is proof. It carries the transaction hash, payer, merchant, amount, nonce and time, plus an attestation: rh777 signs the receipt hash with the same key it settles from. A merchant can prove a payment happened to a third party with a single signature check and no API call.

Retries are safe. A payment settles once per payer nonce. Send the same signed request twice and you get the same receipt back, not a second charge.

The ceiling is yours. The only thing a payer ever approves on chain is a USDG allowance to Permit2. That number is the most any sequence of signatures can move. Set it to what you mean to spend.