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x402 lets you pay per use when credits are exhausted. Request → 402 with quote → pay USDC → retry with receipt.

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Where x402 Applies

SurfaceWhen 402 Happens
Verification APIPOST /api/v1/verification — caller has no credits
Gate check APIGET /api/v1/proofs/check — caller has no credits
MCP toolsTool call returns payment-needed when no credits
Hosted checkoutWhen the embedding app or server makes billable API calls without credits

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Flow

  1. Request — Call verification or gate check.
  2. 402 — API returns 402 Payment Required with quote.
  3. Pay — Pay quoted amount in USDC (e.g., Base).
  4. Retry — Resend request with PAYMENT-SIGNATURE: <receipt>.

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Using x402 Through Verifiers and Checkout

  • Verifiers — Verification consumes credits. If you call the API directly and have no credits, you get 402. Pay, retry with receipt, verification proceeds.
  • Gates — Gate checks consume credits. Use VerifyGate or GET /api/v1/proofs/check. Same flow: no credits → 402 → pay → retry.
  • Hosted checkout — Users at https://neus.network/verify complete verifiers. Payer is resolved server-side (sponsor, gate creator, or user signature). x402 applies when your server makes gate checks or verification calls on behalf of users and runs out of credits.
  • Agents — Delegate with scope: "payments:x402" so the agent can pay per use when acting on your behalf.
PAYMENT-SIGNATURE: <receipt>

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Who Pays (Server Resolution)

  1. x402 receipt — Pay-per-use (you just paid)
  2. Sponsor grant — App-sponsored
  3. Gate billing — Gate creator pays
  4. Signature — User self-pay
  5. No payer — Demo cap (limited free)

Billing and Credits

Credit pricing and payment methods.

Hosted Verify

Checkout URL and verifier params.

MCP Server

x402 in MCP flows.

Agent Delegation

payments:x402 scope.