MonexStock

MonexStock is an agentic stock market on Robinhood Chain. Agents (and humans, at stock.monexprotocol.org) buy official Robinhood tokenized stocks without ever holding gas: you pay USDG through an x402 exact payment (a Permit2 signature — no transaction from your side), Monex Protocol settles it, swaps through the on-chain-verified Uniswap v3 pool, and the router delivers the stock straight to your address, all in one request. If anything fails after your payment settles, you are refunded automatically.

https://www.monexprotocol.org/api/stock

Endpoints

Orders are 1–1000 USDG. Fees are currently zero — the challenge demands exactly the usdg you request. usdg is the amount you spend; the shares you receive float with the pool price, floored by a per-token slippage bound (re-quoted on-chain immediately before execution).

Buy flow for agents

1. Discover — GET /api/stock/list, pick a symbol.
2. Quote (optional) — GET /api/stock/quote?symbol=NVDA&usdg=5.
3. Challenge — POST /api/stock/buy?symbol=NVDA&usdg=5 with no payment header returns 402 with the terms in the body and the payment-required header. accepts[0] carries asset (USDG), amount (atomic, 6 decimals), payTo, and extra.spender (the canonical x402ExactPermit2Proxy).
4. Sign — a Permit2 PermitWitnessTransferFrom EIP-712 signature (domain {name: "Permit2", chainId: 4663}), with permitted = {token: asset, amount}, spender = extra.spender, a random 256-bit nonce, a deadline within 300s, and witness = {to: payTo, validAfter: 0}. No gas is spent.
5. Pay — retry the same POST with the payment-signature header: base64 of {"x402Version": 2, "payload": {"permit2Authorization": {…, "from": "0xYOU"}, "signature": "0x…"}}.
6. Receive — the 200 body reports the order id, the settlement tx, the swap tx, and the exact amount delivered to your address.

The response also carries the standard payment-response header. A 502 after settlement means delivery failed — the body then includes the refund tx.

One-time setup: Permit2 approval

Your wallet needs a one-time USDG approval to Permit2 (0x000000000022D473030F116dDEE9F6B43aC78BA3). If it holds USDG but no ETH for that single approve, request sponsored gas:

curl -X POST https://www.monexprotocol.org/api/gas/sponsor \
  -H 'content-type: application/json' \
  -d '{"address": "0xYOUR_WALLET"}'

Then send approve(0x000000000022D473030F116dDEE9F6B43aC78BA3, max) on the USDG contract. Every payment after that is pure signatures.

Guarantees

• Verified assets only. Each listed token is the official "• Robinhood Token" contract, and swaps route only through the factory-derived USDG pool pinned in config — the pool's token pair and fee are re-verified on-chain before any funds move, so counterfeit tokens and spoofed pools can never be selected.
• Slippage-floored. The swap re-quotes via QuoterV2 at execution and reverts (→ refund) below the per-token floor.
• Refund on failure. USDG settles to the relayer before the swap; any failure after settlement triggers an automatic USDG refund to the payer, and every order is queryable at /api/stock/order/{id}.

Selling back to USDG is coming next.