Cryptorefills x402 — Autonomous Agent Commerce

Fully autonomous purchasing for AI agents with crypto wallets. No accounts, no OAuth, no API keys — just stablecoin and a signing key.

Built on the x402 protocol — HTTP 402 Payment Required as a machine-to-machine payment standard. Two settlement rails are supported: Base (USDC on Ethereum L2, default) and Solana (USDC SPL on Solana mainnet, opt-in).

For human-guided purchases with multiple payment methods, follow cryptorefills-buy instead. For browse-only catalog exploration, follow cryptorefills-catalog instead.

Choose your rail

Default-rail recommendation. If your agent has wallets on both rails and no external constraint, use Base — broader EIP-712 tooling, longer payment window (~15 min vs Solana's ~60 s), and the same byte-identical contract that EVM-only agents have used since v1.0. Use Solana when the agent already runs there, when SOL avoidance matters, or when a registry / marketplace (e.g., pay-skills) demands a Solana-mainnet 402 challenge by default — in that case use the solana.x402.cryptorefills.com host so the rail is host-pinned and unambiguous.

When to Activate

• Agent has a wallet on Base (USDC, EIP-712) or on Solana (USDC SPL, can partial-sign v0 transactions)
• Task requires autonomous purchasing without human payment interaction
• No account setup, OAuth flow, or API key management is desired
• Keywords: "buy with USDC", "USDC SPL", "autonomous purchase", "agent commerce", "x402 payment", "programmatic gift card", "Solana mainnet-beta", "partial-sign", "VersionedTransaction", "compute-budget", "pay-skills registry", "no SOL needed", "no ETH needed"
• Use case: automated gift card procurement, travel eSIM provisioning, programmatic rewards, registry-driven Solana payments

Requirements

Base rail

Solana rail

Spending Safeguards

Autonomous agents spending real money require strict controls:

• Set a per-session spending limit before starting (default: $100 max per session, $50 max per transaction — increase only if the user explicitly requests it).
• Verify the order amount from the 402 response before signing — never sign blindly.
• Use a dedicated wallet per rail with only the necessary stablecoin balance.
• Never log, expose, or share the wallet's private key / secret — use environment variables or a secret manager.
• Log every transaction: order_id, product, amount, wallet address, rail, tx signature/hash.
• Never sign for more than maxAmountRequired in the 402 response.
• Authenticate the 402 before signing anything. payTo is a per-session deposit wallet — the manifest does not list deposit wallets, so an allowlist is impossible. Instead every 402 carries X-Payment-Required-Signature, a JWS (ES256) signed by the gateway. Verify it with the keys from the manifest's attestation.keys / attestation.jwksuri (same origin as the manifest) and require: iss == the origin you POSTed to, sid == the X-Session-Id header, prsha256 == base64url(sha256(PAYMENT-REQUIRED header value exactly as received)), pay_to/network == the decoded accepts[0] values, exp in the future. If the header is absent or any check fails, reject the 402 and do not sign. Full recipe + verify402() snippet: references/protocol.md → Verifying the 402 attestation.

Solana-specific:

• payTo is the OWNER pubkey, NEVER an ATA. Derive the recipient ATA from (payTo, mint). Signing a transfer treating payTo as an ATA will fail.
• Verify extra.feePayer matches the value from PAYMENT-REQUIRED before partial-signing — and use it as the transaction's payerKey.
• Re-fetch recentBlockhash immediately before partial-signing. The validity window is ~60 s; the gateway clamps maxTimeoutSeconds to 60 to flag this. Do not insert user prompts between Phase 1 and Phase 2 on Solana.
• Assert the built transaction has exactly 3 instructions (compute-unit limit, compute-unit price, TransferChecked) before serializing.
• Use SPL TransferChecked (tag 0x0c), not Transfer (0x03). Plain Transfer is rejected by CDP with unknown_error.

General:

• Gift card codes (voucher_code) are cash-like — store securely, never share publicly or write to logs.
• Digital goods are non-refundable once delivered.
• Terms: https://www.cryptorefills.com/terms/

Manifests are served at /.well-known/x402.json on each host and carry an attestation block (signing keys, jwksuri, verify procedure). Read the manifest at the same host you used for Phase 1 — the attestation's iss must equal that origin, and jwksuri must be same-origin with it.

Always send Phase 2 to the same host as Phase 1. The session backing X-Session-Id is host-affine; cross-host POST risks a session lookup miss.

Core Workflow

GET  /v1/brands          → discover brands
GET  /v1/catalog         → get products and prices
POST /v1/orders          → 402 + PAYMENT-REQUIRED + X-Session-Id + X-Payment-Required-Signature
   ↓ verify the attestation (JWS) — reject the 402 if it is missing or invalid
   ↓ sign (EIP-712 for Base, partial-sign v0 tx for Solana)
POST /v1/orders          → submit with PAYMENT-SIGNATURE [+ X-Session-Id] → 200
GET  /v1/orders/{id}     → poll until delivered

The flow, REST contract, and order/delivery model are identical on both rails. Only Phase-1 header selection, the extra block on PAYMENT-REQUIRED, and the signing primitive differ.

Step-by-Step

1. Browse Brands

GET /v1/brands?country_code=us

Returns available brands for the country. Each entry includes brand_name, family, category, min, max.

Country codes are lowercase ISO 3166-1 Alpha-2 (us, it, br) regardless of rail. If receiving a country code from the catalog or buy skills (which use uppercase), convert to lowercase before using x402 endpoints.

2. Get Catalog

GET /v1/catalog?country_code=us&brand_name=Amazon.com

Returns products with productid, isrange, currency, priceusdc, and either denomination (fixed) or minvalue/max_value (range).

• Fixed products (isrange: false): use productid directly. Omit product_value. Face value is denomination in currency units.
• Range products (isrange: true): set items[].productvalue to the desired amount, in the brand's local currency (NOT USD). E.g. for a €5 Amazon.nl card with currency: "EUR", send productvalue: 5. The 402 response will quote the USDC amount to actually settle (typically priceusdc ± a small spread).

Pre-flight: Check stablecoin balance

Before ordering, verify your wallet has sufficient stablecoin on the chosen rail:

• Base: call balanceOf(walletAddress) on 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.
• Solana: call getTokenAccountBalance on the sender ATA — getAssociatedTokenAddress(mint=EPjF…WEGGkZwyTDt1v, owner=agent). No SOL balance needed.

The price_usdc from the catalog is indicative; the exact amount is confirmed in the 402 response.

3. Create Order — Phase 1 (Get Payment Requirements)

Base (default):

curl -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -d '{
    "email": "[email protected]",
    "items": [{
      "product_id": "abc123",
      "beneficiary_account": "[email protected]",
      "product_value": 25
    }]
  }'
# → HTTP 402 with PAYMENT-REQUIRED, X-Session-Id and X-Payment-Required-Signature headers

Solana (header opt-in):

curl -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -H "X-Preferred-Network: solana" \
  -d '<same body>'

Solana (host-pinned):

curl -X POST https://solana.x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -d '<same body>'

productvalue is required for range products; omit for fixed-denomination products. Optional: add "callbackurl": "https://..."; for webhook delivery notifications instead of polling.

Capture three response headers:

• PAYMENT-REQUIRED — base64url-encoded JSON of payment requirements (per-rail shape below).
• X-Session-Id — UUID. Echo on Phase 2 (required for Solana, optional for Base).
• X-Payment-Required-Signature — JWS attesting the two headers above (iss, sid, prsha256, payto, network, exp). Verify before signing — see references/protocol.md. Treat a missing header as a failed 402.

PAYMENT-REQUIRED — Base example

{
  "x402Version": 2,
  "accepts": [{
    "scheme": "exact",
    "network": "eip155:8453",
    "maxAmountRequired": "25000000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": { "name": "USD Coin", "version": "2", "decimals": 6 },
    "payTo": "0x...",
    "description": "$25.00 Amazon Gift Card"
  }],
  "expiresAt": 1830000000
}

Solana deltas vs Base (full Solana example in protocol.md)

4. Sign Payment

Base — EIP-712 / EIP-3009

Sign typed data for transferWithAuthorization.

Domain: USDC contract on Base. Types: TransferWithAuthorization(address from, address to, uint256 value, uint256 validAfter, uint256 validBefore, bytes32 nonce).

See references/protocol.md for exact EIP-712 typed data structure.

Solana — partial-sign v0 transaction

Build a v0 VersionedTransaction with exactly 3 instructions, in order: ComputeBudget set-limit (200_000 units) → ComputeBudget set-price (1000 microLamports) → SPL createTransferCheckedInstruction (tag 0x0c, NOT Transfer 0x03). Use mint = asset, senderAta = getAssociatedTokenAddress(mint, signer), recipientAta = getAssociatedTokenAddress(mint, payTo) (where payTo is the owner), payerKey = extra.feePayer, fresh recentBlockhash from a Solana RPC. Partial-sign with tx.sign([signer]) — leave the feePayer slot for CDP. Serialize ≤ 1232 bytes.

See references/protocol.md for the full recipe.

5. Complete Order — Phase 2

Re-POST the same body with PAYMENT-SIGNATURE. Echo X-Session-Id from Phase 1 (required for Solana).

Base

curl -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <base64url-encoded JSON>" \
  -d '<same body as phase 1>'
# → HTTP 200

PAYMENT-SIGNATURE payload (then base64url-encode the JSON):

{
  "x402Version": 2,
  "scheme": "exact",
  "network": "eip155:8453",
  "payload": {
    "signature": "0x...",
    "authorization": {
      "from": "0xYourWallet",
      "to": "0xPayToAddress",
      "value": "25000000",
      "validAfter": "0",
      "validBefore": "1830000000",
      "nonce": "0xRandomBytes32"
    }
  }
}

Solana

curl -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <base64url-encoded JSON>" \
  -H "X-Session-Id: <UUID from Phase 1 response>" \
  -d '<same body as phase 1>'
# → HTTP 200

PAYMENT-SIGNATURE payload (base64url-encode the outer JSON; the inner payload.transaction is plain base64):

{
  "x402Version": 2,
  "scheme": "exact",
  "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
  "payload": {
    "transaction": "<plain-base64 of serialized v0 transaction>"
  }
}

Encoding rule. The outer PAYMENT-SIGNATURE wrapper is base64url for both rails. Only the inner payload.transaction field on Solana is plain base64 (Solana ecosystem convention; opaque pass-through to the facilitator). Don't unify them.

Server responds with HTTP 200:

{
  "order_id": "cr_abc123",
  "status": "processing",
  "estimated_delivery_seconds": 60,
  "poll_url": "/v1/orders/cr_abc123"
}

6. Track Delivery

GET /v1/orders/{order_id}

Poll every 5–10 seconds until status is completed or failed. Stop polling after 10 minutes and report the order as potentially stuck — contact [email protected] with the order_id.

When completed, the deliveries array contains:

• voucher_code — gift card redemption code
• pin — PIN if required
• url — redemption URL if applicable
• brandname, productname — what was purchased

Worked Example: €5 Amazon.nl gift card on Solana

End-to-end check that the per-step instructions compose. Real numbers, anonymized wallet:

# 1. Discover Amazon.nl
curl 'https://x402.cryptorefills.com/v1/brands?country_code=nl' | jq '.[] | select(.family|test("Amazon"))'
#   → {"brand_name":"Amazon.nl","family":"Amazon.nl","category":"e-commerce", ...}

# 2. Find a range product priced in EUR
curl 'https://x402.cryptorefills.com/v1/catalog?country_code=nl&brand_name=Amazon.nl' | jq '.[0]'
#   → {"product_id":"amzn-nl-range","is_range":true,"currency":"EUR",
#      "min_value":5,"max_value":500,"price_usdc":"5.42", ...}
#   1 EUR isn't offered (min is 5 EUR) — pick 5 EUR.

# 3. Phase 1 — opt into Solana
curl -i -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -H "X-Preferred-Network: solana" \
  -d '{"email":"[email protected]",
       "items":[{"product_id":"amzn-nl-range",
                 "beneficiary_account":"[email protected]",
                 "product_value":5}]}'
#   → HTTP/1.1 402
#      X-Session-Id: 3f9c1a8b-...           ← capture, echo on Phase 2
#      PAYMENT-REQUIRED: <base64url JSON>   ← decode for accepts[0]
#      X-Payment-Required-Signature: <JWS>  ← verify first (protocol.md → Verifying the 402 attestation)
#
#   accepts[0] decoded:
#     network:           solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp
#     asset:             EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v
#     maxAmountRequired: "5420000"          ← 5.42 USDC
#     payTo:             <owner pubkey>     ← derive recipient ATA from this
#     extra.feePayer:    <CDP pubkey>       ← use as transaction.payerKey

// 4. Decode PAYMENT-REQUIRED, verify budget, build the partial-signed v0 tx
import {ComputeBudgetProgram, Connection, Keypair, PublicKey,
        TransactionMessage, VersionedTransaction} from '@solana/web3.js';
import {createTransferCheckedInstruction, getAssociatedTokenAddress} from '@solana/spl-token';
import bs58 from 'bs58';

// 4a. Parse the 402 response
const paymentRequired = JSON.parse(
  Buffer.from(phase1Headers['payment-required'], 'base64url').toString());
const sessionId = phase1Headers['x-session-id'];
const {payTo, asset, maxAmountRequired, extra} = paymentRequired.accepts[0];

// 4b. Spending-safeguard checks BEFORE signing
const SPEND_LIMIT_ATOMIC = BigInt(50_000_000);              // $50 = 50e6 atomic USDC
if (BigInt(maxAmountRequired) > SPEND_LIMIT_ATOMIC) throw new Error('over budget');
if (asset !== 'EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v') throw new Error('wrong mint');

// 4c. Build the transaction
const signer       = Keypair.fromSecretKey(bs58.decode(process.env.SOLANA_SIGNER_KEY));
const conn         = new Connection('https://api.mainnet-beta.solana.com', 'confirmed');
const mint         = new PublicKey(asset);
const owner        = new PublicKey(payTo);                  // OWNER, not an ATA
const feePayer     = new PublicKey(extra.feePayer);         // CDP signs this slot

const senderAta    = await getAssociatedTokenAddress(mint, signer.publicKey);
const recipientAta = await getAssociatedTokenAddress(mint, owner);
const {blockhash}  = await conn.getLatestBlockhash('finalized');  // 'finalized' is older but accepted by all validators — reduces timing sensitivity

const message = new TransactionMessage({
  payerKey:        feePayer,
  recentBlockhash: blockhash,
  instructions: [
    ComputeBudgetProgram.setComputeUnitLimit({units: 200_000}),
    ComputeBudgetProgram.setComputeUnitPrice({microLamports: 1000}),
    createTransferCheckedInstruction(senderAta, mint, recipientAta,
                                     signer.publicKey, BigInt(maxAmountRequired), 6),
  ],
}).compileToV0Message();

const tx = new VersionedTransaction(message);
tx.sign([signer]);                                    // partial — leaves feePayer slot
// Assert on the pre-compilation array — MessageV0 exposes `compiledInstructions`, not `instructions`.
// Reading `tx.message.instructions` throws TypeError. Use the source array passed to TransactionMessage.
if (message.version !== 0) throw new Error('expected v0 message');
if (tx.message.compiledInstructions.length !== 3) throw new Error('expected exactly 3 instructions');
if (tx.serialize().length > 1232) throw new Error('tx too large');

const txB64       = Buffer.from(tx.serialize()).toString('base64');     // inner: plain base64
const inner       = {x402Version: 2, scheme: 'exact',
                     network: 'solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp',
                     payload: {transaction: txB64}};
const headerValue = Buffer.from(JSON.stringify(inner)).toString('base64url');  // outer: base64url

# 5. Phase 2 — same host as Phase 1, echo X-Session-Id from step 3
curl -X POST https://x402.cryptorefills.com/v1/orders \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <headerValue from step 4c>" \
  -H "X-Session-Id: <sessionId from step 4a>" \
  -d '<same body as Phase 1>'
#   → HTTP/1.1 200
#      {"order_id":"cr_xxx","status":"processing","poll_url":"/v1/orders/cr_xxx", ...}

# 6. Poll
curl https://x402.cryptorefills.com/v1/orders/cr_xxx
#   → {"status":"completed",
#      "deliveries":[{"voucher_code":"XXXX-YYYY-ZZZZ","brand_name":"Amazon.nl", ...}]}

If steps 1–6 don't compose for your scenario, the failure is documented in references/troubleshooting.md.

Field Name Mapping (x402 vs MCP)

If switching between x402 and MCP skills, note these field name differences:

Critical Gotchas

Both rails

• Country codes: lowercase for x402 endpoints (us, not US). MCP skills use uppercase — different endpoint, different rule.
• Brand names: case-sensitive — use exact values from /v1/brands response.
• X-Preferred-Network value: case-sensitive lowercase — base or solana only. Base or Solana (capitalized) returns 400 invalid_network on the multi-rail host.
• Amount precision: use the exact maxAmountRequired from 402 — do not round or modify.
• Outer encoding: PAYMENT-SIGNATURE outer wrapper is base64url for both rails (matches the gateway's decoder).
• No rail mixing: a session is pinned to the rail chosen on Phase 1. Don't try to switch rails on Phase 2.
• Same-host Phase 2: POST Phase 2 to the same host you used for Phase 1. Sessions are host-affine.
• Unsigned 402: a 402 without X-Payment-Required-Signature, or whose signature fails any check, must be rejected — never fall back to "the TLS connection looked fine". Hash the PAYMENT-REQUIRED header string as received; do not re-serialise the decoded JSON.

Base

• USDC contract: must be exactly 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base.
• Chain ID: must be 8453 (Base mainnet). Wrong chain = invalid signature.
• Payment timeout: the 402 expiresAt field gives the deadline (~15 min). Sign and resubmit before it expires.
• Nonce: must be unique per transaction. Cryptographically random 32 bytes.
• EIP-712 domain: must match the USDC contract's domain separator on Base.

Solana

• Network string: must be the full CAIP-2 solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp, not "solana" or "solana-mainnet".
• payTo is the OWNER pubkey, not an ATA. The facilitator derives the recipient ATA from (owner, mint).
• Use TransferChecked (0x0c), not Transfer (0x03). CDP rejects the latter with unknown_error.
• Exactly 3 instructions, in order: ComputeBudget set-limit, ComputeBudget set-price, TransferChecked. CDP enforces a 3-to-6 range.
• payerKey = extra.feePayer from PAYMENT-REQUIRED. CDP signs that slot at settle and pays SOL gas.
• Tx packet limit: 1232 bytes. The canonical 3-instruction shape fits comfortably.
• Blockhash window: ~60 s. Re-fetch immediately before partial-signing; do not insert user prompts between Phase 1 and Phase 2.
• Echo X-Session-Id from the Phase 1 response on Phase 2 — required (the SPL transaction is opaque so the gateway has no other way to look up the session).
• Inner encoding: payload.transaction inside the PAYMENT-SIGNATURE JSON is plain base64 (Solana convention) — only the outer wrapper is base64url.

References

Load references only when you need deeper detail than what's in this skill file.