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x402 turns any billable NEUS call into pay-as-you-go. When prepaid credits cannot cover a request, NEUS returns HTTP 402 with a signed quote. Pay the quote, then retry the same request with one header. It is built for agents and machine-to-machine APIs that settle value as they go — no subscription, no human in the loop.

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Flow

1

Call the API

Make your normal request (for example POST /api/v1/verification).
2

Get a 402 + quote

If credits are short, NEUS responds 402 with a quote in the body and the PAYMENT-REQUIRED response header.
3

Pay the quote

Settle in USDC (or native ETH) via POST /api/v1/payments/verify. NEUS returns a one-time payment receipt.
4

Retry with the receipt

Repeat the original call with the receipt in the PAYMENT-SIGNATURE header. The call now succeeds.

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The 402 response

The body carries error.code: "INSUFFICIENT_CREDITS" and an x402 block you can act on directly: 
{
  "success": false,
  "error": { "code": "INSUFFICIENT_CREDITS", "remaining": 0, "required": 4 },
  "x402": {
    "scheme": "x402",
    "requiredCredits": 4,
    "remainingCredits": 0,
    "quote": {
      "quoteId": "…",
      "amountUSD": 0.01,
      "amountCents": 1,
      "creditsNeeded": 4,
      "exp": 1713312300000
    },
    "pay": { "pricing": "/api/v1/payments/pricing" },
    "receiptHeader": "PAYMENT-SIGNATURE"
  }
}
The same quote is also sent as JSON in the PAYMENT-REQUIRED response header. exp is a millisecond timestamp — quotes are short-lived, so pay and retry promptly.

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Pay and retry

# 1. Original call returns 402 with the quote above.
# 2. Settle the quote (USDC or ETH), then retry with the receipt:
curl -X POST https://api.neus.network/api/v1/verification \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <receipt-from-payments-verify>" \
  -d '{ /* the same body as the original request */ }'
Get the receipt by settling the quote through POST /api/v1/payments/verify (type: "x402"). The successful response returns the receipt token and a PAYMENT-RESPONSE header. Each receipt is single-use — reusing one is rejected.

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Payment methods

RailWhere it settles
USDCBase mainnet (eip155:8453), with Ethereum mainnet as fallback
Native ETHNEUS treasury
Card (Stripe) is not used for x402 API billing — it is available for gate checkout. Live unit, minimum, and maximum pricing: GET /api/v1/payments/pricing.

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Agents that pay on their own

Pair x402 with a scoped delegation so an agent can settle calls within a hard cap. This is how autonomous agents settle API calls inside a scoped budget — identity, authority, and payment context in one receipt.
  • Grant agent-delegation with scope: "payments:x402" and a maxSpend cap.
  • maxSpend is a whole-number string in token base units — for USDC (6 decimals), 25 USDC is "25000000". Use toAgentDelegationMaxSpend('25', 6) from @neus/sdk.
  • The agent can pay per call up to the cap; spend beyond it is refused.
Details: Agent delegation.

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Next

Billing

Credits, who pays, and the 402 fallback.

Gate checkout

Charge visitors with USDC or card.

Agent delegation

Spend caps for autonomous agents.
Last modified on June 16, 2026