X402 Bazaar

x402 Bazaar protocol guide for AgentPMT — implement the HTTP 402 two-step handshake, sign EIP-3009 TransferWithAuthorization, route through the AgentPMT facilitator, and settle USDC payments on Base. Use when building agent-to-agent commerce that follows the x402 standard.

Freshness

Last updated: 2026-06-09.

If the current date is more than 7 days after the last updated date, reinstall this skill from skills.sh or ClawHub before relying on endpoints, schemas, setup steps, or examples.

Use this skill when building or debugging the x402 payment flow for AgentPMT credit purchases and agent-to-agent commerce.

Overview

x402 turns HTTP 402 into a machine-payable protocol. AgentPMT uses it to let an external wallet buy USDC-denominated credits, then spend those credits on marketplace tools and workflows.

Handshake

1. Send a purchase request without payment.
2. Read the HTTP 402 response and the PAYMENT-REQUIRED header.
3. Decode the requirements, including payee, amount, token, chain, validity window, and nonce.
4. Sign an EIP-3009 TransferWithAuthorization for USDC on Base.
5. Retry the same purchase with PAYMENT-SIGNATURE.

purchase = {
    "wallet_address": wallet_address,
    "credits": 500,
    "payment_method": "x402",
}
first = requests.post("https://www.agentpmt.com/api/external/credits/purchase", json=purchase, timeout=30)
if first.status_code == 402:
    payment_required = first.headers["PAYMENT-REQUIRED"]
    signed_header = "<base64 signed EIP-3009 authorization>"
    paid = requests.post(
        "https://www.agentpmt.com/api/external/credits/purchase",
        json=purchase,
        headers={"PAYMENT-SIGNATURE": signed_header},
        timeout=30,
    )
    paid.raise_for_status()

Signature Contract

Use the returned x402 fields exactly. The authorization value, validity window, and nonce must match the server challenge. Do not reuse a nonce.

AgentPMT Endpoints

Purpose	Endpoint
Create wallet	POST https://www.agentpmt.com/api/external/agentaddress
Buy credits	POST https://www.agentpmt.com/api/external/credits/purchase
Create session	POST https://www.agentpmt.com/api/external/auth/session
List tools	GET https://www.agentpmt.com/api/external/tools
Invoke tool with credits or direct x402	POST https://www.agentpmt.com/api/external/tools/{productSlug}/actions/{actionSlug}/invoke

EIP-191 Requests After Payment

After credits settle, balance calls and tool calls use wallet-signed EIP-191 messages.

Balance uses the scoped message with an empty payload:

agentpmt-external
wallet:{wallet_lowercased}
session:{session_nonce}
request:{request_id}
action:balance
product:-
payload:

Tool invocation uses the path-bound message:

agentpmt-external
wallet:{wallet_lowercased}
session:{session_nonce}
request:{request_id}
method:POST
path:/external/tools/{productSlug}/actions/{actionSlug}/invoke
payload:{payload_hash}

For a called URL like https://www.agentpmt.com/api/external/tools/google-drive/actions/list-files/invoke, prefer signing path:/external/tools/google-drive/actions/list-files/invoke. Do not sign the host or a query string. AgentPMT also accepts bounded /api, raw-action-slug, and trailing-slash variants only when they resolve to the same product/action.

payload_hash is SHA-256 over the exact action parameters object. Canonical JSON recursively sorts object keys and uses no whitespace; AgentPMT accepts both JS raw UTF-8 serialization and Python escaped serialization (json.dumps(parameters, sort_keys=True, separators=(",", ":"), ensure_ascii=True)). Do not hash wrapper fields like wallet_address, session_nonce, request_id, or signature.

Error Handling

Status	Meaning	Recovery
400	Invalid request or schema mismatch	Rebuild the request from the endpoint schema.
401 EXTERNAL_SIGNATURE_SESSION_NONCE_INVALID	Session nonce is unknown	Create a new session nonce and sign again with a fresh request_id.
401 EXTERNAL_SIGNATURE_SESSION_NONCE_EXPIRED	Session nonce expired	Create a new session nonce and sign again with a fresh request_id.
401 EXTERNAL_SIGNATURE_MALFORMED	Signature could not be recovered	Rebuild the EIP-191 signature from expected_message; do not change parameters after hashing.
401 EXTERNAL_SIGNATURE_WALLET_MISMATCH	Signature recovered a different wallet	Use expected_message, expected_wallet, recovered_wallet_for_expected_message, accepted path candidates, and accepted payload hash forms to correct wallet casing, key selection, path, or canonical JSON.
402	Payment required or insufficient credits	Complete the x402 payment flow.
409 EXTERNAL_SIGNATURE_REQUEST_REPLAY	Replay or duplicate request	Generate a fresh request_id and retry once.
500	Platform or facilitator error	Retry later with a fresh request_id.

Related Skills

• Agent Payment: ../agent-payment
• Agent Tool Marketplace: ../agent-tool-marketplace
• AgentPMT marketplace: https://www.agentpmt.com