# x402 > The legalContext extension, the request commitment, and the x402 pairings. Source: https://lcp.integraledger.com/guides/x402 [x402](https://github.com/coinbase/x402) is HTTP 402 payment: the seller answers a request with a `PaymentRequired` document listing the options it accepts, and the buyer retries with a payment for one of them. This package reads and writes x402 version 2 documents. Import the x402 pieces from `@integraledger/lcp/x402`. ## The `legalContext` extension Every x402 pairing advertises H in the same place: the document's `extensions.legalContext`, as x402's extension mechanism defines it (an `info` object and a JSON Schema for it). ```json no-check { "extensions": { "legalContext": { "info": { "type": "sha256", "value": "0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad", "legalContextUrl": "https://atr.seller.example/0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad" }, "schema": { "$schema": "https://json-schema.org/draft/2020-12/schema", "type": "object" } } } } ``` `LEGAL_CONTEXT` is the extension's key and `LEGAL_CONTEXT_SCHEMA` the full schema every pairing writes. The buyer echoes `extensions` unchanged in its payment, as x402 requires. Where the pairing's payment carries H in nothing public, `info` also carries `legalContextAgreementUrl` ([the agreement URL](https://lcp.integraledger.com/concepts/buyer-gate#the-agreement-url)). One document has one legal context. Each pairing that advertises into the same document with the same H and link leaves it as it is; a different H or link is refused as `x402/legal-context-conflict`. A challenge offering options on several rails therefore carries one H, and the buyer's payment on any of them is bound to the same ATR. ## The request commitment `requestCommitment({ method, target, body })` commits to the request the challenge answers: the method as received, the request-target split at its first `?` into `path` and `query`, and `bodyDigest`, SHA-256 over the body bytes exactly as received. The target is at most 8 KiB of visible ASCII starting with `/`, and the body at most 1 MiB. `tie(accepts, request)` is the ATR's binding slot for every x402 pairing: `["x402", { accepts, request }]`, with every option exactly as issued. `issuedDigest` is SHA-256 over the RFC 8785 form of one option or one commitment, for a seller that keeps a digest of what it issued. ## Advertising several options This example advertises one H into a challenge with two EVM options, one for EIP-3009 and one for Permit2, and shows which pairing serves each option: ```ts import { hash, pairingOf } from "@integraledger/lcp"; import { exactEip3009, exactPermit2, requestCommitment, type PaymentRequired, type PaymentRequirements, } from "@integraledger/lcp/x402"; const base: PaymentRequirements = { scheme: "exact", network: "eip155:84532", amount: "10000", asset: "0x036CbD53842c5426634e7929541eC2318f3dCF7e", payTo: "0x209693Bc6afc0C5328bA36FaF03C514EF312287C", maxTimeoutSeconds: 60, extra: { name: "USDC", version: "2" }, }; const viaPermit2: PaymentRequirements = { ...base, extra: { ...base.extra, assetTransferMethod: "permit2" } }; const doc: PaymentRequired = { x402Version: 2, resource: { url: "https://api.seller.example/v1/quote" }, accepts: [base, viaPermit2], }; const h = await hash(new TextEncoder().encode("the ATR's bytes")); const link = `https://atr.seller.example/${h}`; const first = exactEip3009.advertise(doc, h, link, base); if ("refused" in first) throw new Error(first.code); const both = exactPermit2.advertise(first, h, link, viaPermit2); if ("refused" in both) throw new Error(both.code); console.log(pairingOf(base), pairingOf(viaPermit2)); const read = exactPermit2.read(both); console.log("refused" in read ? read.code : `${read.offer.options.length} option, H ${read.h === h ? "matches" : "differs"}`); const other = await hash(new TextEncoder().encode("another ATR")); const clash = exactPermit2.advertise(first, other, link, viaPermit2); console.log("refused" in clash ? clash.code : "placed"); console.log(await requestCommitment({ method: "POST", target: "/v1/quote?tier=1", body: new TextEncoder().encode("{}") })); ``` ```text x402/exact/eip155/eip3009 x402/exact/eip155/permit2 1 option, H matches x402/legal-context-conflict { method: 'POST', path: '/v1/quote', query: 'tier=1', bodyDigest: '0x44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a' } ``` ## The x402 pairings The x402 pairings, by scheme. The [pairings reference](https://lcp.integraledger.com/reference/pairings) states what each one proves, and [Rails](https://lcp.integraledger.com/guides/rails) gives each rail's field. | Scheme | Pairings | Where H rides | | ------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------- | | `exact` on EVM | `x402/exact/eip155/eip3009`, `x402/exact/eip155/permit2` | The signed authorization's nonce. | | `exact` on EVM, ERC-7710 | `x402/exact/eip155/erc7710-salt`, `x402/exact/eip155/erc7710` | The salt of the redeemed leaf delegation, through MetaMask's DelegationManager; or, where the delegation signs no hash, the echoed extension only. | | `upto` on EVM | `x402/upto/eip155/permit2` | The Permit2 nonce, for a signed maximum. | | `auth-capture` on EVM | `x402/auth-capture/eip155/eip3009`, `x402/auth-capture/eip155/permit2` | The escrow payment's salt, or its salt nonce when the option binds a receiver authorizer or policy. | | `batch-settlement` | `x402/batch-settlement/eip155`, `x402/batch-settlement/solana`, `x402/batch-settlement/cloudflare` | The channel's salt, the opening transaction's memo, or each request's echoed extension. See [Channels, sessions and subscriptions](https://lcp.integraledger.com/guides/sessions). | | `exact` on other rails | Solana, Stellar, XRPL, Hedera, Algorand, Aptos, Cardano, Casper, Concordium, NEAR, Polkadot Asset Hub, Starknet, Sui, Tron, TON, Lightning | Each rail's own field; see [Rails](https://lcp.integraledger.com/guides/rails). | | `upto` on Solana | `x402/upto/solana` | The Memo instruction of the transaction that opens a one-request payment channel. | ## Building on x402 `build(choice, h)` takes the document, the chosen option, the payer's account and the time in Unix seconds: ```ts no-check interface X402Choice { required: PaymentRequired; accepted: PaymentRequirements; from: Hex; now: number; } ``` It returns what the buyer's signer signs, in the rail's own form, and `complete`, which turns the signer's answer into the x402 payment. On `x402/exact/eip155/eip3009` that is EIP-712 typed data; on the other EVM pairings a request whose `kind` names the form (`"eip712"`, or `"erc7710"` for a delegation); on other rails a transaction or message to sign. ## Reading the payment `bound(payment)` reads H from the payment; `reference(payment)` gives the keys to find its settlement; `status(ref, reader)` reads the settlement through an `EvmReader` you supply, which answers three JSON-RPC calls: `eth_getTransactionReceipt`, `eth_getBlockByNumber` for the `safe` and `finalized` marks, and `eth_getTransactionByHash`. A reader that throws `ReaderError`, or answers for another network, leaves the payment pending, never failed. `pairingOfPayment(payment)` names the pairing that serves a presented EVM payment.