Keeping the record

The gate does not store anything. After a payment, what you keep is your proof of what you agreed to.

What to keepCopy Anchor Link

Keep the bytes as bytes. Re-encoding them as a parsed and re-serialised JSON document changes the hash.

Confirm a payment later: checkCopy Anchor Link

check(bytes, presented, binding, landed?) answers one question: is the ATR hash the pairing reads from this payment the SHA-256 of these bytes? A payment from which the pairing reads no ATR hash is declined signed-not-bound. It fetches nothing and calls no signer.

import { check, transact, type Fetch, type Signer } from "@integraledger/terms";
import { exactEip3009 } from "@integraledger/lcp/x402";
import { privateKeyToAccount } from "viem/accounts";

const atr = new TextEncoder().encode(
  '{"atrVersion":"1","id":"0f8fad5b-d9cb-469f-a165-70867728950e","x402":{"z":1.0,"a":"caf\\u00e9"},"seller":{"note":"Café — 30 días ✓"}}',
);
const H = "0x8b1e122580ae3f6a8c3d36a24294e1260a87bde70f597279b973e39310072938";
const link = `https://atr.seller.example/${crypto.randomUUID()}`;
const offer = {
  x402Version: 2,
  resource: { url: "https://api.seller.example/v1/quote" },
  accepts: [
    {
      scheme: "exact",
      network: "eip155:84532",
      amount: "10000",
      asset: "0x036CbD53842c5426634e7929541eC2318f3dCF7e",
      payTo: "0x209693Bc6afc0C5328bA36FaF03C514EF312287C",
      maxTimeoutSeconds: 60,
      extra: { name: "USDC", version: "2" },
    },
  ],
  extensions: { legalContext: { info: { type: "sha256", value: H, legalContextUrl: link }, schema: {} } },
};
const fetch: Fetch = async (url) => (url === link ? new Response(atr) : new Response(null, { status: 404 }));
const wallet = privateKeyToAccount("0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80");
const signer: Signer = {
  account: `eip155:84532:${wallet.address}`,
  async sign(request) {
    if (request.kind !== "eip712") throw new Error(request.kind);
    return wallet.signTypedData(request.typedData as Parameters<typeof wallet.signTypedData>[0]);
  },
};

const paid = await transact(offer, exactEip3009, signer, fetch);
if ("decline" in paid || "approve" in paid || paid.signed === null) throw new Error("not paid");

// Later: the payment against the bytes you kept, and against a record that differs by one byte.
const kept = await check(paid.bytes, paid.signed, exactEip3009);
const other = new TextEncoder().encode(new TextDecoder().decode(paid.bytes).replace("30 días", "31 días"));
const altered = await check(other, paid.signed, exactEip3009);

console.log("kept bytes   ", "decline" in kept ? kept.decline.code : kept.h);
console.log("altered bytes", "decline" in altered ? altered.decline.code : altered.h);

kept bytes    0x8b1e122580ae3f6a8c3d36a24294e1260a87bde70f597279b973e39310072938
altered bytes signed-not-bound

Where finish or transact returned landed, pass it beside the payment: check(bytes, signed, binding, landed). The caller passes as landed only the receipt its own reader read for the payment, as finish or transact returned it, never a value another party sent. A landed member written into the payment is not read.

For a pairing whose payment is not a public proof of H, check reads the payment as it reads any other: it confirms that the hash the pairing reads from it is the SHA-256 of the kept bytes, and declines signed-not-bound where the pairing reads none. That payment does not prove H in public. The proof of H is the agreement payment, which is itself a public-proof payment: check it with the binding of the pairing it was paid with.

The gate returns the agreement's receipt as agreement, not the signed agreement payment. The receipt is the agreement URL's statement: the gate checks that it names H and is a recorded agreement, and does not look up the transaction it names. Keep it, and confirm H from that transaction on network: for an EIP-3009 agreement payment, the nonce of the token's AuthorizationUsed event is H.

A moved paymentCopy Anchor Link

A decline that carries moved means your signer moved the payment itself before the gate declined: a Lightning node paid the invoice, or a signer broadcast a transaction. It also means, in the agreement exchange, that the gate sent the agreement payment and then declined. moved holds the payment as signed, the ATR's bytes and their hash.

• Keep all three, as you would keep a payment that succeeded.
• For the payment for the resource, present moved.signed to the seller again rather than signing a new payment.
• For an agreement payment, call again without approved to collect its receipt, never with approved: every call with approved signs and sends a new agreement payment. See agreement payments.
• Whether to deal with the seller another way is your principal's decision.

A payment still settlingCopy Anchor Link

If the seller answers that your payment is still settling, send the same payment again. Never sign a new one: the payment already carries H, and a second signature is a second payment.