> ## Documentation Index > Fetch the complete documentation index at: https://developers.circle.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}. > Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts. > Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md. > Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md. > Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers. > Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews. > Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming. > Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md. > Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors. > API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product. > Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes. > When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records. > Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md. # Verify an x402 payment > Verifies the buyer's signed authorization and the payment payload without creating a payment, consuming keyless trial usage, or submitting anything onchain. Use before [Settle an x402 payment](/api-reference/facilitator-service/all/settle-payment) to catch problems early. For `upto`, `amount` must equal the maximum the buyer signed. Example signatures come from a public test key. Never fund it. ## OpenAPI ````yaml openapi/facilitator-service.yaml post /v1/facilitator/x402/verify openapi: 3.0.3 info: title: Facilitator Service version: 1.0.0 description: > Facilitator Service is Circle's hosted x402 facilitator. Sellers call Facilitator Service to verify and settle x402 payments in USDC on Arc, Base, and Polygon PoS without operating their own relayer, gas wallet, or sanctions screening. Facilitator Service implements the x402 v2 `exact` scheme and settles USDC through EIP-3009 authorizations. Facilitator Service also implements the x402 v2 `upto` scheme. With `upto`, the buyer signs a Permit2 authorization for a maximum amount, and the seller settles the actual amount, from zero up to that maximum. The buyer either approves the Permit2 contract onchain or attaches a signed EIP-2612 permit through the `eip2612GasSponsoring` extension, which needs no buyer transaction. `/supported` lists the networks where `upto` is available. servers: - url: https://api.circle.com description: Production security: - CircleApiKey: [] - FacilitatorSellerProof: [] tags: - name: Payments description: | x402 payment verification, settlement, and status. - name: Supported payment kinds description: | x402 payment kinds and extensions Facilitator Service accepts. paths: /v1/facilitator/x402/verify: post: tags: - Payments summary: Verify an x402 payment description: > Verifies the buyer's signed authorization and the payment payload without creating a payment, consuming keyless trial usage, or submitting anything onchain. Use before [Settle an x402 payment](/api-reference/facilitator-service/all/settle-payment) to catch problems early. For `upto`, `amount` must equal the maximum the buyer signed. Example signatures come from a public test key. Never fund it. operationId: VerifyPayment requestBody: required: true content: application/json: schema: type: object required: - x402Version - paymentPayload - paymentRequirements properties: x402Version: type: integer enum: - 2 description: >- x402 protocol version. Facilitator Service supports version 2. paymentPayload: $ref: '#/components/schemas/PaymentPayload' paymentRequirements: $ref: '#/components/schemas/PaymentRequirements' examples: exact: summary: Exact payment description: Verifies a 1 USDC `exact` payment on Arc testnet. value: x402Version: 2 paymentPayload: x402Version: 2 resource: url: https://api.example.com/premium description: Premium report mimeType: application/json accepted: scheme: exact network: eip155:5042002 amount: '1000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 12 extra: name: USDC version: '2' assetTransferMethod: eip3009 payload: signature: >- 0x15e13cbd896cdf88f30cb826b2e79b97a35280b2ab459a1f50cd64ee48034e2849e7445b14feadcc3d1bb2868b41e8cf7997b623daa73872509c7027194765311b authorization: from: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' to: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' value: '1000000' validAfter: '0' validBefore: '1791400000' nonce: >- 0x4d3f8a2c9b1e7f60d5a4c3b2e1f0a9b8c7d6e5f4a3b2c1d0e9f8a7b6c5d4e3f2 extensions: payment-identifier: info: required: true id: pay_5f0d3c1a9b7e4d2c paymentRequirements: scheme: exact network: eip155:5042002 amount: '1000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 12 extra: name: USDC version: '2' assetTransferMethod: eip3009 upto: summary: Upto payment description: >- Verifies an `upto` payment with a 5 USDC maximum on Arc testnet. `amount` equals the signed maximum. The buyer has already approved Permit2. value: x402Version: 2 paymentPayload: x402Version: 2 resource: url: https://api.example-seller.com/llm/completions description: Metered LLM completion mimeType: application/json accepted: scheme: upto network: eip155:5042002 amount: '5000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 300 extra: name: USDC version: '2' assetTransferMethod: permit2 facilitatorAddress: '0x2240278661b83f55D31B2506F77266f6fFd21D55' payload: signature: >- 0xc73bf42ff0307a07972c5d07349a289d34270ad4298454b66c41a1fbe6a5a13e22f516c1cc85c884e41d77db7ea4c6a8b1b8271c1012022962e5af0601a52e341b permit2Authorization: from: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' permitted: token: '0x3600000000000000000000000000000000000000' amount: '5000000' spender: '0x4020A4f3b7b90ccA423B9fabCc0CE57C6C240002' nonce: '1791399400123456' deadline: '1791400300' witness: to: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' facilitator: '0x2240278661b83f55D31B2506F77266f6fFd21D55' validAfter: '1791399400' extensions: payment-identifier: info: required: true id: pay_5f0d3c1a9b7e4d2c paymentRequirements: scheme: upto network: eip155:5042002 amount: '5000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 300 extra: name: USDC version: '2' assetTransferMethod: permit2 facilitatorAddress: '0x2240278661b83f55D31B2506F77266f6fFd21D55' uptoGasSponsored: summary: Upto payment with a gasless Permit2 approval description: >- Same `upto` payment, with an `eip2612GasSponsoring` permit that approves Permit2 for exactly the signed maximum, so the buyer needs no approval transaction. value: x402Version: 2 paymentPayload: x402Version: 2 resource: url: https://api.example-seller.com/llm/completions description: Metered LLM completion mimeType: application/json accepted: scheme: upto network: eip155:5042002 amount: '5000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 300 extra: name: USDC version: '2' assetTransferMethod: permit2 facilitatorAddress: '0x2240278661b83f55D31B2506F77266f6fFd21D55' payload: signature: >- 0xc73bf42ff0307a07972c5d07349a289d34270ad4298454b66c41a1fbe6a5a13e22f516c1cc85c884e41d77db7ea4c6a8b1b8271c1012022962e5af0601a52e341b permit2Authorization: from: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' permitted: token: '0x3600000000000000000000000000000000000000' amount: '5000000' spender: '0x4020A4f3b7b90ccA423B9fabCc0CE57C6C240002' nonce: '1791399400123456' deadline: '1791400300' witness: to: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' facilitator: '0x2240278661b83f55D31B2506F77266f6fFd21D55' validAfter: '1791399400' extensions: payment-identifier: info: required: true id: pay_5f0d3c1a9b7e4d2c eip2612GasSponsoring: info: from: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' asset: '0x3600000000000000000000000000000000000000' spender: '0x000000000022D473030F116dDEE9F6B43aC78BA3' amount: '5000000' nonce: '0' deadline: '1791400300' signature: >- 0x30d1893d3332db1f1f73076c6f43c2ea35eba2b999eec11003e7cf6577566cf1182fec72031187a0f8a40e1af5ed4b5267be572fd7800e0a7ff4f6653e0861e71b version: '1' paymentRequirements: scheme: upto network: eip155:5042002 amount: '5000000' asset: '0x3600000000000000000000000000000000000000' payTo: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: 300 extra: name: USDC version: '2' assetTransferMethod: permit2 facilitatorAddress: '0x2240278661b83f55D31B2506F77266f6fFd21D55' responses: '200': description: Verification result content: application/json: schema: $ref: '#/components/schemas/VerifyResponse' '400': description: Malformed request body. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '401': description: > Missing or invalid authentication. Returned when: - Neither a valid Circle API key nor a valid seller proof is present. - The seller proof does not match the payment's `network` and `payTo`. - The seller proof's nonce has been replayed with a different digest. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '412': description: > `upto` only. Returned when all of the following are true: - The buyer's USDC balance covers the signed maximum. - The buyer's Permit2 allowance for `0x000000000022D473030F116dDEE9F6B43aC78BA3` is below the signed maximum. - The request carries no usable `eip2612GasSponsoring` permit (the extension is absent or has no signed fields). The body carries the `permit2_allowance_required` reason. An insufficient balance returns `insufficient_funds` instead. To proceed, the buyer either approves Permit2 onchain or attaches a signed `eip2612GasSponsoring` permit, which needs no buyer transaction. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '415': description: Unsupported content encoding. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '429': description: Rate limit exceeded. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '500': description: Unexpected internal error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '503': description: > A required service is temporarily unavailable. For `upto`, also returned when verification is at capacity. Retry with backoff. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - CircleApiKey: [] - FacilitatorSellerProof: [] components: schemas: PaymentPayload: type: object description: > x402 v2 payment payload. Includes the payment terms the buyer accepted and the signed authorization for the USDC transfer: an EIP-3009 authorization for `exact`, or a Permit2 authorization for `upto`. For `upto`, the payload sent to `/settle` must match the payload sent to `/verify`. The seller can only vary `paymentRequirements.amount` between calls. required: - x402Version - accepted - payload properties: x402Version: type: integer enum: - 2 description: x402 protocol version. Facilitator Service supports version 2. resource: $ref: '#/components/schemas/ResourceInfo' accepted: $ref: '#/components/schemas/PaymentRequirements' payload: description: > Signed buyer authorization. Facilitator Service reads it according to `paymentRequirements.scheme`. oneOf: - $ref: '#/components/schemas/ExactPayload' - $ref: '#/components/schemas/UptoPayload' extensions: type: object description: > Optional x402 extensions. Facilitator Service recognizes `payment-identifier` on every scheme and `eip2612GasSponsoring` on `upto`. Use `payment-identifier` to scope idempotency to your seller account. The value carries an `info` object with `required` and `id` fields. `id` must be 16 to 128 characters from `[A-Za-z0-9_-]`. An `info` object without an `id` is treated as if the extension were absent. additionalProperties: true properties: eip2612GasSponsoring: $ref: '#/components/schemas/EIP2612GasSponsoring' example: payment-identifier: info: required: true id: pay_5f0d3c1a9b7e4d2c PaymentRequirements: type: object description: > Payment terms the seller advertises for an x402 resource. Facilitator Service validates that the buyer's authorization matches these requirements. required: - scheme - network - amount - asset - payTo - maxTimeoutSeconds properties: scheme: type: string enum: - exact - upto description: > Payment scheme. Facilitator Service supports `exact` and `upto`. `upto` is available only on the networks where `/supported` lists an `upto` kind. network: type: string description: > CAIP-2 network identifier. Must match one of the blockchains Facilitator Service supports. See [Supported networks](/facilitator-service/supported-networks). example: eip155:5042002 amount: type: string description: > Payment amount in atomic USDC units. USDC uses 6 decimals, so `1000000` equals 1 USDC. For `upto`, the meaning depends on the endpoint. On verify, `amount` must equal the maximum the buyer signed. On settle, `amount` is the actual amount to charge, from `0` up to that maximum. Facilitator Service checks the buyer's USDC balance and Permit2 allowance against this amount. example: '1000000' asset: type: string description: | USDC contract address on the target network. example: '0x3600000000000000000000000000000000000000' payTo: type: string description: The seller's payout address on the target network. example: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' maxTimeoutSeconds: type: integer description: > Maximum time in seconds Facilitator Service may wait for the settlement to reach a terminal state before returning a pending response. example: 12 extra: type: object description: > Scheme-specific parameters. For the `exact` scheme with EIP-3009, Facilitator Service expects `name`, `version`, and `assetTransferMethod`. For the `upto` scheme, the `upto` kind in `/supported` advertises `name`, `version`, `assetTransferMethod: permit2`, and `facilitatorAddress`. Buyers sign `facilitatorAddress` into `witness.facilitator`. additionalProperties: true example: name: USDC version: '2' assetTransferMethod: eip3009 VerifyResponse: type: object required: - isValid - payer properties: isValid: type: boolean description: Whether the payload passed every check before submission. example: true invalidReason: type: string description: Reason code. Present when `isValid` is false. enum: - invalid_x402_version - unsupported_scheme - invalid_network - invalid_payment_requirements - invalid_payload - invalid_exact_evm_payload_recipient_mismatch - invalid_exact_evm_payload_authorization_value_mismatch - invalid_exact_evm_payload_authorization_valid_after - invalid_exact_evm_payload_authorization_valid_before - invalid_exact_evm_payload_signature - invalid_transaction_state - insufficient_funds - invalid_permit2_spender - invalid_permit2_recipient_mismatch - permit2_token_mismatch - permit2_amount_mismatch - permit2_not_yet_valid - permit2_deadline_expired - upto_facilitator_mismatch - invalid_permit2_signature - permit2_invalid_nonce - invalid_eip2612_extension_format - eip2612_from_mismatch - eip2612_asset_mismatch - eip2612_spender_not_permit2 - eip2612_deadline_expired - permit2_2612_amount_mismatch - permit2_simulation_failed example: invalid_exact_evm_payload_signature payer: type: string description: > Buyer address recovered from the signed authorization. Always rendered, including on invalid results, so callers can correlate. example: 0x9aE2... ErrorResponse: type: object required: - code - message properties: code: type: integer description: HTTP status code echoed in the body for programmatic handling. example: 403 message: type: string description: >- Human-readable summary of the error, suitable for display to end users. example: Registration required to continue settling on this address errors: type: array description: Per-issue reason codes. items: type: object required: - reason properties: reason: type: string description: | Machine-readable reason code. enum: - registration_required - authorization_expired - payment_identifier_conflict - credential_bound_elsewhere - credential_payer_conflict - authorization_reused - permit2_allowance_required example: registration_required ResourceInfo: type: object description: | Optional metadata about the resource the buyer is paying for. properties: url: type: string description: URL of the paid resource. example: https://api.example.com/premium description: type: string description: Human-readable description of the resource. example: Premium report mimeType: type: string description: MIME type the resource returns. example: application/json ExactPayload: type: object description: Signed payload for the `exact` scheme. required: - signature - authorization properties: signature: type: string description: > Buyer's EIP-3009 signature over the `TransferWithAuthorization` typed data, signed under the USDC contract's EIP-712 domain for the payment's network. example: 0x... authorization: $ref: '#/components/schemas/EIP3009Authorization' UptoPayload: type: object description: Signed payload for the `upto` scheme. required: - signature - permit2Authorization properties: signature: type: string description: > Buyer's signature over the Permit2 `PermitWitnessTransferFrom` typed data, signed under the Permit2 EIP-712 domain for the payment's network. Accepts EOA signatures and signatures from deployed ERC-1271 smart accounts. example: 0x... permit2Authorization: $ref: '#/components/schemas/Permit2Authorization' EIP2612GasSponsoring: type: object description: > `upto` only. Signed EIP-2612 permit that approves the Permit2 contract to spend the buyer's USDC, so the buyer needs no onchain approval transaction. The permit's fields are always checked against the payload. Its nonce and signature are checked onchain only when the buyer's Permit2 allowance is below the payment amount. An attached permit is always submitted with the settlement. The Permit2 proxy skips a permit that fails onchain. required: - info properties: info: type: object description: > When any of `from`, `asset`, `spender`, `amount`, `nonce`, `deadline`, or `signature` is present, all seven are required, and a partial or malformed set returns `invalid_eip2612_extension_format`. An `info` with none of them, such as an echo of the seller's declaration, is treated as if the extension were absent. properties: from: type: string description: > Permit owner. Must equal `permit2Authorization.from`, otherwise `eip2612_from_mismatch`. example: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' asset: type: string description: > USDC contract address. Must equal `permit2Authorization.permitted.token`, otherwise `eip2612_asset_mismatch`. example: '0x3600000000000000000000000000000000000000' spender: type: string description: > Approved spender. Must be the Permit2 contract (`0x000000000022D473030F116dDEE9F6B43aC78BA3`), otherwise `eip2612_spender_not_permit2`. example: '0x000000000022D473030F116dDEE9F6B43aC78BA3' amount: type: string description: > Permit value in atomic USDC units. Must equal the signed Permit2 maximum (`permitted.amount`), otherwise `permit2_2612_amount_mismatch`. example: '5000000' nonce: type: string description: > The buyer's current EIP-2612 nonce on the USDC contract, as a decimal string. When the permit is needed and the nonce does not match onchain, the result is `permit2_simulation_failed`. example: '0' deadline: type: string description: > Unix timestamp after which the permit expires. Separate from the Permit2 `deadline`. Must be at least 10 seconds in the future, otherwise `eip2612_deadline_expired`. example: '1791400300' signature: type: string description: > 65-byte signature over the USDC contract's EIP-2612 `Permit` typed data, under the USDC EIP-712 domain for the payment's network. When the permit is needed and the signature is invalid, the result is `permit2_simulation_failed`. example: >- 0x30d1893d3332db1f1f73076c6f43c2ea35eba2b999eec11003e7cf6577566cf1182fec72031187a0f8a40e1af5ed4b5267be572fd7800e0a7ff4f6653e0861e71b version: type: string description: Extension version. Facilitator Service does not validate it. example: '1' EIP3009Authorization: type: object description: > EIP-3009 `TransferWithAuthorization` message the buyer signed. Facilitator Service submits this authorization to the USDC contract to move funds from `from` to `to`. required: - from - to - value - validAfter - validBefore - nonce properties: from: type: string description: Buyer's address (source of the USDC transfer). example: 0x9aE2... to: type: string description: > Recipient address. Must equal `paymentRequirements.payTo` for Facilitator Service to accept the authorization. example: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' value: type: string description: > Transfer amount in atomic USDC units. Must equal `paymentRequirements.amount`. example: '1000000' validAfter: type: string description: Unix timestamp before which the authorization is not valid. example: '0' validBefore: type: string description: Unix timestamp after which the authorization is no longer valid. example: '2208988800' nonce: type: string description: > Unique 32-byte value that binds this authorization to one specific transfer. Reusing a nonce that already settled returns `invalid_transaction_state`. example: 0x4d3f... Permit2Authorization: type: object description: > Permit2 `PermitWitnessTransferFrom` message the buyer signed for the `upto` scheme. The buyer signs a maximum amount, and you settle any amount from zero up to that maximum. Facilitator Service submits this authorization to the x402 `upto` Permit2 proxy from the facilitator wallet named in `witness.facilitator`. required: - from - permitted - spender - nonce - deadline - witness properties: from: type: string description: > Buyer's address (the Permit2 owner and source of the USDC transfer). The buyer's USDC allowance for the Permit2 contract must cover the payment amount, or the request must carry an `eip2612GasSponsoring` permit. Otherwise Facilitator Service returns HTTP 412. example: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266' permitted: type: object description: Token and maximum amount the buyer authorizes. required: - token - amount properties: token: type: string description: | USDC contract address. Must equal `paymentRequirements.asset`. example: '0x3600000000000000000000000000000000000000' amount: type: string description: > Maximum transfer amount in atomic USDC units. Must be greater than zero. On verify, must equal `paymentRequirements.amount`. On settle, `paymentRequirements.amount` must not exceed it. example: '5000000' spender: type: string description: > Address of the x402 `upto` Permit2 proxy contract that Facilitator Service calls to settle. example: '0x4020A4f3b7b90ccA423B9fabCc0CE57C6C240002' nonce: type: string description: > Permit2 unordered nonce as a uint256 decimal string. A nonce already used onchain returns `permit2_invalid_nonce`. example: '1791399400123456' deadline: type: string description: > Unix timestamp after which the authorization is no longer valid. Must be at least 10 seconds in the future when Facilitator Service checks it. example: '1791400300' witness: type: object description: Extra terms the buyer binds into the Permit2 signature. required: - to - facilitator - validAfter properties: to: type: string description: | Recipient address. Must equal `paymentRequirements.payTo`. example: '0x7c3ea945Fc4253255d8260fc18c2dee3D8C5dD3A' facilitator: type: string description: > Facilitator wallet allowed to submit the settlement. Take this from `extra.facilitatorAddress` on the `upto` kind in `/supported`. Addresses are compared case-insensitively. example: '0x2240278661b83f55D31B2506F77266f6fFd21D55' validAfter: type: string description: Unix timestamp before which the authorization is not valid. example: '1791399400' securitySchemes: CircleApiKey: type: http scheme: bearer description: > Bearer token authentication with a Circle API key. Use this for production settlement. Settling with an API key also binds the `payTo` to your Circle account, which ends the keyless trial allowance. FacilitatorSellerProof: type: apiKey in: header name: Facilitator-Seller-Proof description: > Base64url-encoded envelope carrying an EIP-712 signature that proves the caller controls the `payTo` address. Use this for the keyless trial, before you settle with a Circle API key. Settling an `upto` payment requires a Circle API key. ````