Merchants

Sell to agents whose owners trust them to buy.

Join in five minutes. No code until the last step, and no change to your prices.

Two modes, both built.

Covered runs on Base mainnet today for any x402 service, with no integration. Native is built and tested: you add the middleware, register with registerMerchant, and are paid from escrow when the window closes. No third-party Native merchant is live yet.

Covered mode

Live on Base mainnet

Undo pays any x402 service. No integration.

Undo pays the merchant through standard x402 and keeps your USDC in escrow. The merchant does not need to know Undo exists. Every mainnet proof so far is a Covered order.

Works with any x402 endpoint, today.
Automatic refund on errors, timeouts, empty responses and double charges.
One-hour dispute window, then the payment settles.

Native mode

Built and tested

The merchant is the escrow receiver.

Built and covered by tests, ready for merchants who want it. No third-party Native merchant is live yet.

Add @undo/sdk/middleware in front of your route. Hono and Express adapters.
Register on-chain with registerMerchant. It is permissionless.
Receive the funds from escrow when the dispute window closes.
Accept or contest each refund. Contested cases go to the arbiter.

What joining changes.

Agents prefer services marked as protected.
You are the escrow receiver. Undo never holds your sales.
You choose the dispute window and the instant refund cap.
Every case is yours to accept or contest.

The middleware.

It checks that a call was paid into escrow for exactly this request. You get a tailored copy after joining.

server.ts (Hono)

import { createOnchainCaseReader, undoHono } from "@undo/sdk/middleware";

const undo = undoHono({
  gateway: "0x0ED3EE2B783Bd1B7752E97e2B8FFF59C05c3a8E9",
  readCase: createOnchainCaseReader({
    rpcUrl: "https://mainnet.base.org",
    operator: "0xA47aa1C3cc3684861E4aC27d5Ff07825C5e76B62",
  }),
});

// Undo calls pass; anything else falls through to x402.
app.use("/paid/*", undo);

server.ts (Express)

import express from "express";
import { createOnchainCaseReader, undoExpress } from "@undo/sdk/middleware";

app.use("/paid", express.raw({ type: "*/*" }), undoExpress({
  gateway: "0x0ED3EE2B783Bd1B7752E97e2B8FFF59C05c3a8E9",
  readCase: createOnchainCaseReader({ rpcUrl: "https://mainnet.base.org", operator: "0xA47aa1C3cc3684861E4aC27d5Ff07825C5e76B62" }),
}));

Your dashboard.

Orders, refunds and open cases for your payout address.