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x402 ProtocolOverview

x402 protocol — Inzi Facilitator

x402 is an open payment standard (Coinbase / X402 Foundation) that embeds stablecoin payments directly into HTTP requests using the 402 Payment Required status code.

Inzi is an x402 facilitator — verify and settle payments across Polygon, Base, Ethereum, Tron, and TON. More chains than any other facilitator.

How x402 works

  1. Client requests a protected resource
  2. Server responds 402 with X-PAYMENT-REQUIRED header (amount, token, payTo address)
  3. Client pays on-chain to the payTo address
  4. Client retries with X-PAYMENT header (tx proof)
  5. Server calls Inzi facilitator to verify → 200 OK

This enables machine-to-machine payments, AI agent commerce, and pay-per-API billing — no subscriptions, no API keys for the payer.

Quick integration

Install the SDK

npm install @inzi/x402

Add middleware to your API

import express from 'express'
import { x402 } from '@inzi/x402/express'
 
const app = express()
 
// Protect endpoint with x402 paywall ($0.01 USDC on Base)
app.get('/api/catalog', x402({
  apiKey: 'sk_live_xxxxx',    // Your Inzi API key
  amount: '0.01',
  asset: 'USDC',
  network: 'base',
}), (req, res) => {
  // req.x402Payment contains verified payment data
  res.json({ catalog: ['item1', 'item2'] })
})

That’s it

Requests without payment get 402. Requests with valid X-PAYMENT header get 200.

Facilitator API

If you want to build your own middleware or use a different framework, call the facilitator API directly:

Get config

curl https://api.inzilink.com/api/v1/x402/config \
  -H "Authorization: Bearer sk_live_xxxxx"

Returns payTo addresses per chain, supported networks and assets.

Verify payment

curl -X POST https://api.inzilink.com/api/v1/x402/verify \
  -H "Authorization: Bearer sk_live_xxxxx" \
  -H "Content-Type: application/json" \
  -d '{
    "payment": {
      "txHash": "0xabc...",
      "chain": "base",
      "token": "USDC",
      "amount": "0.01",
      "payerAddress": "0x...",
      "payTo": "0x..."
    },
    "requirements": {
      "scheme": "exact",
      "network": "base",
      "maxAmountRequired": "0.01",
      "asset": "USDC",
      "resource": "/api/catalog"
    }
  }'

Response: { "valid": true, "txHash": "0x...", "verifiedAt": "..." }

Supported chains

ChainTokensAvg verification
PolygonUSDC, USDT~6 seconds (3 blocks)
BaseUSDC~6 seconds
EthereumUSDC, USDT~36 seconds
TronUSDT~10 seconds
TONUSDT~5 seconds

Inzi supports Tron and TON — the two largest stablecoin networks outside of Ethereum. No other x402 facilitator does this.

Why Inzi as facilitator?

  • Multi-chain: 5 networks vs Coinbase CDP’s 3
  • Existing infrastructure: battle-tested scanners, RPC fallback, settlement workers
  • Merchant dashboard: see x402 payments in the same dashboard as checkout payments
  • Same API key: use your existing sk_live_ key — no new account needed
  • Settlement: funds are settled to your wallet automatically
Getting Started