Open APIs V2

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Verify Payment (V2)

Code
POST /papi/v2/b402/verify

Validates a signed payment payload off-chain. No gas is consumed and no on-chain transaction is submitted. Use this endpoint to check that a payment is well-formed and the signature is valid before calling /settle.

Differences from V1 (/papi/v1/b402/verify):

V1	V2
x402Version: 1	x402Version: 2 (strict — any other value rejected with invalid_x402_version)
paymentPayload.scheme / paymentPayload.network at top level	removed — client echoes the chosen requirement via paymentPayload.accepted
—	paymentPayload.resource promoted to top level of paymentPayload
paymentRequirements.scheme: "exact" only	paymentRequirements.scheme must be "exact" or "upto"; any other value rejected with invalid_scheme
extra.facilitatorAddress	replaced by extra.signerAddress + extra.spenderAddress
invalidMessage in response	omitted from wire by default; populated only for structural-error codes (invalid_payload, invalid_payment_requirements)

Request Body

Field	Type	Mandatory	Remarks
x402Version	integer	Yes	Must be 2. Any other value → invalid_x402_version.
paymentPayload	object	Yes	The signed payment payload
paymentPayload.x402Version	integer	Yes	Protocol version (should match top-level x402Version)
paymentPayload.resource	object	No	ResourceInfo object describing the resource the payment grants access to (x402 v2 §5.1). Optional per spec but strongly recommended for traceability.
paymentPayload.resource.url	string	Yes *	URL of the protected resource. *Required when paymentPayload.resource is present.
paymentPayload.resource.description	string	No	Human-readable description of the resource
paymentPayload.resource.mimeType	string	No	MIME type of the expected response
paymentPayload.accepted	object	Yes	The PaymentRequirements kind the client has chosen to fulfill (echoed from /supported)
paymentPayload.accepted.scheme	string	Yes	"exact" or "upto". Any other value → invalid_scheme.
paymentPayload.accepted.network	string	Yes	CAIP-2 network identifier
paymentPayload.accepted.amount	string	Yes	Required payment amount in atomic units
paymentPayload.accepted.asset	string	Yes	Token contract address
paymentPayload.accepted.payTo	string	Yes	Merchant wallet address
paymentPayload.accepted.maxTimeoutSeconds	integer	Yes	Maximum settlement timeout in seconds
paymentPayload.accepted.extra	object	Yes	Optional per x402 v2 spec; required in b402 because extra.assetTransferMethod drives handler dispatch.
paymentPayload.accepted.extra.name	string	Yes	Token EIP-712 domain name
paymentPayload.accepted.extra.version	string	Yes	Token EIP-712 domain version
paymentPayload.accepted.extra.assetTransferMethod	string	Yes	"eip3009", "permit2-exact", or "permit2-upto"
paymentPayload.accepted.extra.signerAddress	string	Yes	Facilitator EOA (from /supported)
paymentPayload.accepted.extra.spenderAddress	string	Conditional	Permit2 proxy contract (from /supported). Required for permit2-*; absent for eip3009.
paymentPayload.payload	object	Yes	Signature + authorization details
paymentPayload.payload.signature	string	Yes	EIP-712 signature (0x-prefixed hex, 65 bytes)
paymentPayload.payload.authorization	object	Conditional	EIP-3009 only. Required when assetTransferMethod == "eip3009".
paymentPayload.payload.authorization.from	string	Conditional	Payer wallet address
paymentPayload.payload.authorization.to	string	Conditional	Recipient wallet address
paymentPayload.payload.authorization.value	string	Conditional	Amount in atomic units
paymentPayload.payload.authorization.validAfter	string	Conditional	Unix timestamp (seconds) — signature valid after
paymentPayload.payload.authorization.validBefore	string	Conditional	Unix timestamp (seconds) — signature valid before
paymentPayload.payload.authorization.nonce	string	Conditional	Unique nonce (32-byte hex)
paymentPayload.payload.permit2Authorization	object	Conditional	Permit2 only. Required when assetTransferMethod is "permit2-exact" or "permit2-upto".
paymentPayload.payload.permit2Authorization.permitted.token	string	Conditional	Token contract address
paymentPayload.payload.permit2Authorization.permitted.amount	string	Conditional	Maximum authorised amount (atomic units)
paymentPayload.payload.permit2Authorization.from	string	Conditional	Payer (token owner) address — signer of the Permit2 signature
paymentPayload.payload.permit2Authorization.spender	string	Conditional	Must match accepted.extra.spenderAddress
paymentPayload.payload.permit2Authorization.nonce	string	Conditional	Permit2 nonce
paymentPayload.payload.permit2Authorization.deadline	string	Conditional	Unix timestamp (seconds) when the permit expires
paymentPayload.payload.permit2Authorization.witness	object	Conditional	Witness data included in the EIP-712 signed message
paymentPayload.payload.permit2Authorization.witness.to	string	Conditional	Recipient address. Must match accepted.payTo. Enforced on-chain by the proxy contract.
paymentPayload.payload.permit2Authorization.witness.facilitator	string	Conditional	Facilitator EOA bound to this authorisation. permit2-upto only; absent for permit2-exact.
paymentPayload.payload.permit2Authorization.witness.validAfter	string	Conditional	Earliest Unix timestamp (seconds) at which the transfer can execute. "0" means immediately.
paymentPayload.extensions	object	No	x402 v2 extensions object. Set extensions.bazaar to make your endpoint discoverable via B402 Bazaar. Send {} or omit if unused.
paymentRequirements	object	Yes	Expected payment requirements from the resource server. Same shape as paymentPayload.accepted.
paymentRequirements.scheme	string	Yes	"exact" or "upto". Any other value → invalid_scheme.
paymentRequirements.network	string	Yes	CAIP-2 network identifier
paymentRequirements.amount	string	Yes	Required payment amount in atomic units
paymentRequirements.asset	string	Yes	Token contract address
paymentRequirements.payTo	string	Yes	Merchant wallet address
paymentRequirements.maxTimeoutSeconds	integer	Yes	Maximum settlement timeout in seconds (x402 v2 spec §5.1.2)
paymentRequirements.extra	object	Yes	Optional per x402 v2 spec; required in b402 because extra.assetTransferMethod drives handler dispatch. Must match a kind from /supported; same fields as paymentPayload.accepted.extra.

Merchant responsibility — forwarding extra to buyers: The merchant MUST populate paymentRequirements.extra (and the identical paymentPayload.accepted.extra) with values copied from the matching kinds[] entry in the /supported response. In particular, extra.signerAddress and extra.spenderAddress (for permit2-*) must be surfaced to the buyer in the upstream HTTP 402 response — buyers have no other channel to discover them. Omitting them will cause buyer-side signing to fail or produce signatures that B402 rejects with invalid_payload. See Forwarding Addresses to Buyers.

Conditional fields: Required depending on assetTransferMethod:

• eip3009 → payload.authorization.* required; payload.permit2Authorization must be absent.
• permit2-exact / permit2-upto → payload.permit2Authorization.* required; payload.authorization must be absent.
• permit2-upto only → payload.permit2Authorization.witness.facilitator additionally required; it must equal extra.signerAddress.

Signing permit2-exact: The stock @x402/evm client does not ship a Permit2 signer. See the Permit2 Signing Guide for the EIP-712 typed data shape and TypeScript reference (viem / ethers.js).

Example — EIP-3009

Code
{
  "x402Version": 2,
  "paymentPayload": {
    "x402Version": 2,
    "resource": {
      "url": "https://api.example.com/premium/data",
      "description": "Premium API access",
      "mimeType": "application/json"
    },
    "accepted": {
      "scheme": "exact",
      "network": "eip155:56",
      "amount": "1000000",
      "asset": "0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d",
      "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
      "maxTimeoutSeconds": 300,
      "extra": {
        "name": "USD Coin",
        "version": "2",
        "assetTransferMethod": "eip3009",
        "signerAddress": "0x1111111111111111111111111111111111111111"
      }
    },
    "payload": {
      "signature": "0xf3746613c2d920b5fdabc0856f2aeb2d4f88ee6037b8cc5d04a71a4462f134801234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef1b",
      "authorization": {
        "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
        "to": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
        "value": "1000000",
        "validAfter": "0",
        "validBefore": "1710000600",
        "nonce": "0x1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef"
      }
    }
  },
  "paymentRequirements": {
    "scheme": "exact",
    "network": "eip155:56",
    "amount": "1000000",
    "asset": "0x8AC76a51cc950d9822D68b83fE1Ad97B32Cd580d",
    "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
    "maxTimeoutSeconds": 300,
    "extra": {
      "name": "USD Coin",
      "version": "2",
      "assetTransferMethod": "eip3009",
      "signerAddress": "0x1111111111111111111111111111111111111111"
    }
  }
}

Example — Permit2 Exact (any ERC-20)

Code
{
  "x402Version": 2,
  "paymentPayload": {
    "x402Version": 2,
    "resource": {
      "url": "https://api.example.com/premium/data",
      "description": "Premium API access",
      "mimeType": "application/json"
    },
    "accepted": {
      "scheme": "exact",
      "network": "eip155:56",
      "amount": "5000000",
      "asset": "0x55d398326f99059ff775485246999027b3197955",
      "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
      "maxTimeoutSeconds": 300,
      "extra": {
        "name": "Tether USD",
        "version": "1",
        "assetTransferMethod": "permit2-exact",
        "signerAddress": "0x1111111111111111111111111111111111111111",
        "spenderAddress": "0x2222222222222222222222222222222222222222"
      }
    },
    "payload": {
      "signature": "0xaabbccdd...65bytes...eeff",
      "permit2Authorization": {
        "permitted": {
          "token": "0x55d398326f99059ff775485246999027b3197955",
          "amount": "5000000"
        },
        "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
        "spender": "0x2222222222222222222222222222222222222222",
        "nonce": "1",
        "deadline": "1710000600",
        "witness": {
          "to": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
          "validAfter": "0"
        }
      }
    }
  },
  "paymentRequirements": {
    "scheme": "exact",
    "network": "eip155:56",
    "amount": "5000000",
    "asset": "0x55d398326f99059ff775485246999027b3197955",
    "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
    "maxTimeoutSeconds": 300,
    "extra": {
      "name": "Tether USD",
      "version": "1",
      "assetTransferMethod": "permit2-exact",
      "signerAddress": "0x1111111111111111111111111111111111111111",
      "spenderAddress": "0x2222222222222222222222222222222222222222"
    }
  }
}

Example — Permit2 Upto (pay-as-you-go)

Code
{
  "x402Version": 2,
  "paymentPayload": {
    "x402Version": 2,
    "resource": {
      "url": "https://ai.example.com/api/v1/chat",
      "description": "AI Agent API - per-request billing",
      "mimeType": "application/json"
    },
    "accepted": {
      "scheme": "upto",
      "network": "eip155:56",
      "amount": "100000000",
      "asset": "0x55d398326f99059ff775485246999027b3197955",
      "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
      "maxTimeoutSeconds": 300,
      "extra": {
        "name": "Tether USD",
        "version": "1",
        "assetTransferMethod": "permit2-upto",
        "signerAddress": "0x1111111111111111111111111111111111111111",
        "spenderAddress": "0x3333333333333333333333333333333333333333"
      }
    },
    "payload": {
      "signature": "0x112233...65bytes...4455",
      "permit2Authorization": {
        "permitted": {
          "token": "0x55d398326f99059ff775485246999027b3197955",
          "amount": "100000000"
        },
        "from": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e",
        "spender": "0x3333333333333333333333333333333333333333",
        "nonce": "5",
        "deadline": "1710086400",
        "witness": {
          "to": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
          "facilitator": "0x1111111111111111111111111111111111111111",
          "validAfter": "0"
        }
      }
    }
  },
  "paymentRequirements": {
    "scheme": "upto",
    "network": "eip155:56",
    "amount": "100000000",
    "asset": "0x55d398326f99059ff775485246999027b3197955",
    "payTo": "0x8B3a350e2f3E6B9cC6FB10Fd106bA08f08bec5D2",
    "maxTimeoutSeconds": 300,
    "extra": {
      "name": "Tether USD",
      "version": "1",
      "assetTransferMethod": "permit2-upto",
      "signerAddress": "0x1111111111111111111111111111111111111111",
      "spenderAddress": "0x3333333333333333333333333333333333333333"
    }
  }
}

In this example, the buyer authorised up to 100 USDT ("100000000"). The actual amount to charge is specified later in the /settle call via the settleAmount field.

Response Body

Field	Type	Presence	Remarks
isValid	boolean	Always	Whether the payment payload is valid
payer	string	Always	Recovered payer wallet address from the signature
invalidReason	string	Only when isValid=false	x402 v2 standard error code. See table below.
invalidMessage	string	Only for structural-error codes	Human-readable debug context. Populated only when invalidReason ∈ {invalid_payload, invalid_payment_requirements}. Absent for all other codes (spec-strict).

invalidMessage is populated only when invalidReason is a structural-error code (invalid_payload, invalid_payment_requirements) — i.e., the request shape itself is malformed. Spec-strict codes (signature/authorization failures, insufficient_funds) carry no invalidMessage; debug context for those is retained in server logs only.

Example — Valid Payment

Code
{
  "code": "000000",
  "message": "success",
  "data": {
    "isValid": true,
    "payer": "0x742d35Cc6634C0532925a3b844Bc454e4438f44e"
  }
}

Example — Invalid Payment

Code
{
  "code": "000000",
  "message": "success",
  "data": {
    "isValid": false,
    "invalidReason": "invalid_exact_evm_payload_signature",
    "payer": "0x0000000000000000000000000000000000000000"
  }
}

Notes:

• An invalid payment still returns HTTP 200 with code: "000000". Check the isValid field in data for the verification outcome. HTTP-level errors (400 / 401 / etc.) indicate request-level problems (missing parameters, authentication failure, etc.).
• /verify is read-only and off-chain. It can be called repeatedly at no cost.
• In permit2-upto mode, /verify checks that the authorised cap covers amount. The actual settlement amount (which may be lower) is specified in the subsequent /settle call via the settleAmount field.
• Calling /verify before /settle is recommended but not mandatory. If you skip /verify, the /settle endpoint will still validate the payment before executing it.

Envelope Rejection Rules

The following envelope-level checks run before payload validation. They short-circuit with a fixed invalidReason regardless of the remainder of the request:

Condition	invalidReason
Request body missing / unparseable	invalid_payload
x402Version missing or != 2	invalid_x402_version
paymentRequirements.scheme is set and not in {"exact","upto"}	invalid_scheme
paymentPayload.accepted.scheme is set and not in {"exact","upto"}	invalid_scheme

invalidReason / errorReason Values

The V2 endpoints emit x402 v2 standard error codes. invalidReason appears on /verify responses; errorReason on /settle responses (see /settle — Settle Payment).

Value	Phase	Description
insufficient_funds	verify	Payer token balance below required amount
invalid_exact_evm_payload_signature	verify	EIP-712 / Permit2 signature invalid
invalid_exact_evm_payload_authorization_valid_after	verify	Authorization not yet valid
invalid_exact_evm_payload_authorization_valid_before	verify	Authorization expired
invalid_exact_evm_payload_authorization_value_mismatch	verify	Authorized amount below required
invalid_exact_evm_payload_recipient_mismatch	verify	authorization.to / witness.to does not match payTo
invalid_network	verify	Network not supported
invalid_payload	verify	Payload malformed or internal field mismatch
invalid_payment_requirements	verify	Payment requirements structurally invalid
invalid_scheme	both	scheme is neither "exact" nor "upto"
unsupported_scheme	—	Reserved per x402 v2 spec §9; not currently emitted by b402 (we use invalid_scheme for scheme-validation failures).
invalid_x402_version	both	x402Version is not 2
invalid_transaction_state	settle	On-chain revert or confirmation timeout
unexpected_verify_error	verify	Internal verify error (unmapped)
unexpected_settle_error	settle	Internal settle error (e.g. RPC failure, unmapped)

Deviations from x402 v2 spec

B402 V2 aligns with the x402 v2 public spec on wire format. The following are deliberate b402 extensions — they are not spec violations; they occupy slots the spec explicitly reserves for implementations, or add functionality the spec doesn't yet cover.

Deviation	Rationale
POST /supported (spec uses GET)	The Binance Open API gateway signs every request body with merchant RSA; a body-less GET would require reworking the auth model. POST with empty JSON {} preserves the gateway's signing pattern.
"upto" scheme	Spec only defines "exact". B402 adds "upto" for pay-as-you-go flows where the buyer authorises a cap and the merchant charges an actual amount ≤ cap.
assetTransferMethod: "permit2-exact" / "permit2-upto"	Spec only describes EIP-3009 for "exact". B402 adds Permit2-based methods (mainstream ERC-20 pattern) via the inline extra.assetTransferMethod selector.
settleAmount field on /settle request	Required for permit2-upto: buyer signs an authorised cap; the merchant specifies the actual settled amount at /settle time. Ignored for other methods. Not present in spec.
extra.assetTransferMethod / signerAddress / spenderAddress	B402-specific fields inside the spec-reserved extra slot (spec: "Scheme-specific additional information"). Replaces V1's overloaded facilitatorAddress with two explicit fields (EOA signer vs Permit2 spender contract).

Apart from these, all wire shapes, field names, error codes, and semantics follow the x402 v2 spec. Merchants can write integration code against the public spec and only the deviations above require b402-specific handling.

Note on settleAmount for permit2-upto

The x402 v2 spec (§7.2) describes the upto scheme as reusing paymentRequirements.amount to mean "maximum authorized amount at verification time, but the actual amount to settle at settlement time" — i.e., the merchant re-submits paymentRequirements at /settle with amount mutated to the actual charge.

B402 uses a dedicated settleAmount field on the /settle request instead. Rationale: keeps paymentRequirements immutable across the verify → settle flow, which is cleaner for logging, auditability, and replay protection. Functionally equivalent; just a different encoding choice.

Integrators should:

• Send paymentRequirements.amount = the signed cap (same value at both /verify and /settle)
• Include settleAmount on the /settle body for permit2-upto (must be ≤ paymentRequirements.amount)
• Omit settleAmount for eip3009 / permit2-exact (or include it; it's ignored — the full signed amount is always transferred)