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Every deployed resource serves a single paid entry point, POST /call, fronted by a trusted sidecar (the gate). An unpaid call returns HTTP 402 with a machine-readable quote; a paid call carries a signed authorization in the X-PAYMENT header. This page is the wire reference. The model behind it is the escrow response gate.

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Free paths

These paths are un-gated and matched exactly. Everything else requires payment.

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POST /call

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string
required
Must be application/json.
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object
required
A JSON body matching the resource’s OpenAPI request schema.
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string
A base64-encoded payment payload. Omit it to receive the 402 quote; include it to pay.

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Unpaid call: HTTP 402

A POST /call with no X-PAYMENT header returns HTTP 402 and a quote describing how to pay.
The accepts array may carry a second exact entry for the flat EIP-3009 path.
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number
Always 2.
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string
Why the call was refused.
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array
One entry per acceptable scheme.
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string
utter-escrow for the gated metered path.
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string
eip155:5042002 (Arc Testnet).
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string
The cap, in USDC base units. This is the ceiling the buyer signs, not the price.
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string
The USDC token address.
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string
The PaymentEscrow contract address.
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string
The resourceId (bytes32) the debit is bound to.
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number
How long the buyer’s authorization must stay valid.
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object
The metered pricing terms: model, base, perKB, computeMultiplier, optional maxResponseBytes, optional errorPrice.
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object
The EIP-712 domain to sign under: name UtterEscrow, version 1, chainId 5042002, verifyingContract the escrow address.
Re-POST the same request with an X-PAYMENT header carrying the base64 encoding of this payload:
X-PAYMENT payload (before base64)
The authorization is signed as an EIP-712 DebitAuthorization under the UtterEscrow domain.

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Outcomes

On success the X-PAYMENT-RESPONSE header carries a base64 receipt:
X-PAYMENT-RESPONSE receipt (before base64)

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Size caps

The gate never runs the handler against an unreserved authorization, and it never debits on anything but a validated success. See the escrow response gate and metering and classification.