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Cover image for The day I gave an AI a wallet — building an approval-gated shopping agent with Sonnet 4.6, AgentCore Payments, Rakuten and Stripe
Yuuki Yamashita
Yuuki Yamashita

Posted on • Originally published at github.com

The day I gave an AI a wallet — building an approval-gated shopping agent with Sonnet 4.6, AgentCore Payments, Rakuten and Stripe

#bedrock #agentcorepayments #nextjs #ai

TL;DR
I built a PoC that wires up Bedrock AgentCore Payments (x402 + USDC) and Rakuten + Stripe Checkout behind a single Strands Agent — and made sure the agent can't spend a single cent without a human approval card. Production-deployed on Vercel, with an 8-language UI.

Why I built this

I have five different talks / CFPs lined up — re:Invent 2026 COM Track, Qiita Tech Festa, iOSDC LT, re:Deploy Security, and a Slack Hackathon — all centred on the same idea: "the day you give an AI a wallet, and what an approval gate looks like."

Slides alone weren't going to carry the message. I needed a shared implementation base that I could spin up live in front of an audience.

The shape of the goal was simple:

User asks something in natural language → the agent picks an option → an approval card pops up → human approves / rejects → on approval, the actual payment runs → result is summarised back to the user.

I wanted to prove this in two axes: pay-per-call paid APIs (microtransactions) and real-world product purchases.

Architecture

  • Frontend: Next.js 16 on Vercel (approval list + chat + checkout result)
  • State: DynamoDB — wallet_agent_tasks / approvals / txns, Streams + PITR
  • Agent: AgentCore Runtime (ARM64 container) + Strands Agent + Claude Sonnet 4.6
  • Payments — Phase 1: AgentCore Payments → Privy (StripePrivy) → x402 → base-sepolia USDC
  • Payments — Phase 2: Rakuten Ichiba IchibaItem/Search → Stripe Checkout (test mode)
  • Localisation: ja / en / zh / ko / fr / it / es / ar (RTL) — 8 languages, localStorage + navigator.language auto-detect, LINE Seed JP Bold as the base font

All of it — code, CloudFormation, demo script — lives in yama3133/wallet-agent.

The agent itself

The agent is just six @tool functions wired into a Strands Agent.

@tool
def search_paid_resources(query: str = "") -> list[dict]: ...  # x402 catalog

@tool
def request_payment_approval(resource_id: str, amount_usd: str, justification: str) -> dict:
    """Write a pending approval to DynamoDB / local JSON and block until a decision lands."""

@tool
def execute_x402_payment(resource_id: str, payment_session_id: str | None = None) -> dict:
    """Drive AgentCore Payments' generate_payment_header through to a successful x402 settle."""

@tool
def search_rakuten_items(keyword: str, max_jpy: int | None = None, hits: int = 5) -> list[dict]: ...

@tool
def request_purchase_approval(item_id: str, title: str, amount_jpy: int, justification: str) -> dict: ...

@tool
def execute_stripe_checkout(item_id: str, title: str, amount_jpy: int, image_url: str = "") -> dict:
    """Create a Stripe Checkout Session and return the URL."""
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The trick is that request_*_approval writes a row to DynamoDB and waits. The tool chain literally can't progress until a human flips the row to APPROVED. That single primitive keeps the LLM from going off the rails.

Phase 1 — the AgentCore Payments signer trap

This is where I lost the most time.

ProcessPayment → AccessDeniedException
"Privy credentials are invalid. Please verify the credential configuration."
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I could create PaymentManager, PaymentConnector, and PaymentInstrument (an Embedded Crypto Wallet) from boto3 just fine. ProcessPayment was the one call that wouldn't go through.

Looking at the Privy dashboard, the wallet that AWS's CreatePaymentInstrument had created was owned by an internally-generated Privy User, and my Authorization Key was not registered as a signer on any wallet at all.

The fix is to run Privy's official template, privy-io/aws-agentcore-sdk, locally and click through the "Connect agent" UI in a browser. That UI hits Privy's internal API and adds your Authorization Key to additional_signers on the wallet.

git clone https://github.com/privy-io/aws-agentcore-sdk ~/wallet-agent-privy-template
cd ~/wallet-agent-privy-template
# Drop NEXT_PUBLIC_PRIVY_APP_ID / PRIVY_APP_SECRET / NEXT_PUBLIC_PRIVY_SIGNER_ID into .env.local
pnpm dev
# → browse to localhost:3001 → log in → Connect agent
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After that, process_payment returns PROOF_GENERATED and the merchant (https://drvd12nxpcyd5.cloudfront.net/market-recap, a public x402 demo endpoint) accepts the payload.

[bedrock_agentcore.payments.manager] Successfully processed payment for user test-user-yama3133
[bedrock_agentcore.payments.manager] Successfully generated payment header for user test-user-yama3133
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The lesson: you cannot finish AgentCore Payments setup purely server-side. Design your demo flow with the Privy frontend baked in from day one.

Phase 2 — Rakuten and the Referer pitfall

Phase 2 was a much more pedestrian WebAPI face-plant.

I registered a new Rakuten webservice application, took the Application ID (UUID form), and hit https://openapi.rakuten.co.jp/ichibams/api/IchibaItem/Search/20260401. Got:

{"errors":{"errorCode":403,"errorMessage":"REQUEST_CONTEXT_BODY_HTTP_REFERRER_MISSING"}}
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Adding Referer: https://wallet-agent.vercel.app/ didn't help. The actual culprit was User-Agent bot detection — User-Agent: wallet-agent/0.1 is rejected. Swapping to a browser-ish Mozilla/5.0 ... makes the request go through.

The final tools/rakuten.py looks like this:

headers = {
    "User-Agent": (
        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) "
        "AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36"
    ),
    "Referer": referer,             # WALLET_AGENT_PUBLIC_URL
    "Origin": referer.rstrip("/"),
}
if access_key:
    headers["accessKey"] = access_key
    params["accessKey"] = access_key
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From there: a pair of black socks at ¥1,980, a Stripe Checkout Session, test card 4242 4242 4242 4242, and a redirect to https://wallet-agent.vercel.app/checkout/success?session_id=cs_test_... showing "Paid / 1,980 JPY."

DynamoDB and the Vercel frontend

The approval state lives in wallet_agent_approvals on DynamoDB. Local dev falls back to agent/.approvals.json — flipped by WALLET_AGENT_STORAGE=local|dynamo.

The Next.js 16 App Router side is a small handful of route handlers:

// /api/approvals (GET) — list PENDING
const r = await ddb().send(new ScanCommand({
  TableName: TABLES.approvals,
  FilterExpression: "#s = :p",
  ExpressionAttributeNames: { "#s": "status" },
  ExpressionAttributeValues: { ":p": "PENDING" },
}));

// /api/approvals/[id] (POST) — decide
await ddb().send(new UpdateCommand({
  TableName: TABLES.approvals,
  Key: { approval_id: id },
  UpdateExpression: "SET #s = :d, decision = :d, #r = :r, decided_at = :t",
  ExpressionAttributeNames: { "#s": "status", "#r": "reason" },
  ExpressionAttributeValues: { ":d": body.decision, ":r": body.reason ?? "", ":t": String(Date.now()/1000), ":pending": "PENDING" },
  ConditionExpression: "attribute_exists(approval_id) AND #s = :pending",
}));
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I bit the error is a DynamoDB reserved word trap once — you need ExpressionAttributeNames: { "#e": "error" } to update it, otherwise you get ValidationException: Invalid UpdateExpression.

8-language UI and LINE Seed JP

apps/web/src/lib/i18n.ts is just a flat dictionary of 8 languages × 31 keys, wired into a tiny useI18n() Context. The Arabic locale flips document.documentElement.dir to "rtl":

useEffect(() => {
  document.documentElement.lang = locale;
  document.documentElement.dir = getDir(locale); // "ltr" | "rtl"
}, [locale]);
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The font is LINE Seed JP Bold via next/font/google, exposed as a CSS variable --font-line-seed and dropped into Tailwind's font-sans. It gives Japanese text a friendly rounded-bold feel that reads well alongside the LINE-app universe.

Things I learned

  1. The Privy signer wall is not solvable server-side. Build the "Connect agent" frontend step into the demo on day one.
  2. agentcore configure is interactive by default. With -ni, a hand-rolled ECR repo, and a Dockerfile in the bundle, you can drive it from CI just fine.
  3. Vercel's 60-second Hobby timeout does not play nicely with synchronously invoking a long-running agent. Plan for waitUntil or a polling pattern.
  4. One "human approval card" tool is enough to make the LLM safe-by-construction. The same primitive solves Phase 1 and Phase 2 without modification.

Links

This PoC is meant to power five different talks with one shared implementation. I'll be improving it as those events get closer. Feedback welcome.

— @yama3133 (AWS Community Builder, AI Engineering / 2026)

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