Buy through a merchant agent

https://your-running-build/api/embed/{deploymentId}/mcp

{
  "payments": [
    {
      "sessionId": "acs_example",
      "approval": { "cartVersion": 1, "totalAmount": 15.81, "currency": "SGD" }
    }
  ]
}

A2A_BASE_URL=https://your-running-build \
A2A_DEPLOYMENT_ID=<published-customer-deployment-id> \
A2A_ORIGIN=https://your-allowed-client-origin \
yarn tsx scripts/a2a/mcp-smoke-test.ts

A2A_BASE_URL=https://your-running-build \
A2A_DEPLOYMENT_ID=<published-customer-deployment-uuid> \
yarn tsx scripts/a2a/smoke-test.ts

import { ClientFactory, JsonRpcTransportFactory } from "@a2a-js/sdk/client";
import { AgentCard, Message, SendMessageRequest } from "@a2a-js/sdk";

const headers = { Origin: origin, Authorization: `Bearer ${token}` };
const factory = new ClientFactory({
  transports: [
    new JsonRpcTransportFactory({
      fetchImpl: (url, init) =>
        fetch(url, {
          ...init,
          headers: {
            ...Object.fromEntries(new Headers(init?.headers)),
            ...headers,
          },
        }),
    }),
  ],
});
const card = AgentCard.fromJSON(await (await fetch(cardUrl)).json());
const checkoutEnabled = card.skills.some((skill) =>
  skill.tags.includes("checkout"),
);
const client = await factory.createFromAgentCard(card);
const task = await client.sendMessage(
  SendMessageRequest.fromJSON({
    message: Message.toJSON(
      Message.fromJSON({
        messageId: crypto.randomUUID(),
        role: "ROLE_USER",
        contextId: sessionId,
        parts: [
          {
            text: checkoutEnabled
              ? "Find two suitable items, deliver to SG, and prepare an offer."
              : "Find two suitable items and show their purchase links.",
          },
        ],
      }),
    ),
    configuration: { returnImmediately: true },
  }),
);

import { importJWK, jwtVerify, decodeProtectedHeader } from "jose";

const { signing_keys } = await (
  await fetch(`${baseUrl}/.well-known/ucp`)
).json();
const { kid } = decodeProtectedHeader(offer.checkoutJwt);
const key = signing_keys.find((candidate) => candidate.kid === kid);
const { payload } = await jwtVerify(
  offer.checkoutJwt,
  await importJWK(key, "ES256"),
  {
    issuer: baseUrl,
    subject: offer.sessionId,
  },
);

const response = await fetch(
  `${baseUrl}/api/embed/${deploymentId}/checkout-sessions/pay`,
  {
    method: "POST",
    headers: { ...headers, "Content-Type": "application/json" },
    body: JSON.stringify({
      sessionId: offer.sessionId,
      approval: {
        cartVersion: offer.cartVersion,
        totalAmount: offer.totalAmount,
        currency: offer.currency,
      },
    }),
  },
);
if (!response.ok) throw new Error("Card checkout could not be opened.");
const { checkoutUrl } = await response.json();
// Present checkoutUrl to the buyer for card entry on Stripe's hosted page.

await fetch(`${baseUrl}/api/embed/${deploymentId}/checkout-sessions/complete`, {
  method: "POST",
  headers: { ...headers, "Content-Type": "application/json" },
  body: JSON.stringify({
    sessionId: offer.sessionId,
    idempotencyKey: paymentRequestId,
    approval: {
      cartVersion: offer.cartVersion,
      totalAmount: offer.totalAmount,
      currency: offer.currency,
    },
    paymentProof, // ACP shared payment token or configured x402 proof
  }),
});