Core Infrastructure

RelAI Facilitator

The execution layer for x402 payments.

Verifies payments, settles them on-chain, and abstracts gas — so your API never needs to handle blockchain complexity.

ClientAPI402signs paymentFacilitator verifiesFacilitator settlesAPI returns 200

The facilitator sits between the payment signature and the blockchain — handling everything in between.

What is a facilitator?

A facilitator is a service that:

verifies payment signatures
prevents replay attacks
submits transactions on-chain
confirms settlement

It acts as a payment processor for x402 — exactly like Stripe, but instead of cards and banks, it uses crypto signatures and blockchains.

Why you need it

Without a facilitator
✗ run blockchain infrastructure
✗ verify signatures manually
✗ handle nonces & replay protection
✗ submit transactions
✗ pay gas fees
With a facilitator
call /verify and /settle
no blockchain infra needed
gas sponsored automatically
replay protection built-in

The facilitator does not hold funds

Non-custodial by design

The facilitator only executes payments that were already authorized by the user's signature. It cannot move funds without a valid, user-signed authorization. Your funds remain under your control at all times.

RelAI Facilitator

RelAI provides a hosted facilitator that:

works across multiple chains (Solana, Base, Avalanche, Polygon, Ethereum, SKALE)
sponsors gas fees — users only pay in USDC
exposes standard endpoints (/verify, /settle)
integrates directly with the x402 SDK
Facilitator endpoint
https://facilitator.x402.fi

Architecture

ClientCalls protected resources and constructs payment payloads
Resource ServerAdvertises payment requirements, delegates verify/settle to facilitator
FacilitatorVerifies signatures, executes settlement on-chain, sponsors gas
BlockchainExecutes and confirms the actual token transfer

Step by step

01User requests resource — GET to protected API endpoint
02API returns 402 — payment required with x402 v2 response
03User signs authorization — off-chain EIP-3009 or SPL signature (free, no gas)
04Client sends payment — payload with signed authorization
05API calls facilitator — POST /settle
06Facilitator executes — transferWithAuthorization(), gas sponsored by RelAI
07API returns resource — 200 OK

Supported Networks

NetworkTokenStandardGas
SKALE BITE V2USDCEIP-3009sFUEL (sponsored)
SKALE BaseUSDCEIP-3009CREDIT (sponsored)
BaseUSDCEIP-3009ETH (sponsored)
AvalancheUSDCEIP-3009AVAX (sponsored)
PolygonUSDCEIP-3009POL (sponsored)
EthereumUSDCEIP-3009ETH (sponsored)
SolanaUSDCSPL TokenSOL (sponsored)

API Reference

Base URL: https://facilitator.x402.fi

GET /supported

Returns all supported payment schemes, networks, and signer addresses.

response
{
  "kinds": [
    { "x402Version": 2, "scheme": "exact",     "network": "eip155:8453",  "extra": { "feePayer": "0x1892...", "decimals": 6 } },
    { "x402Version": 2, "scheme": "svm-exact", "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp", "extra": { "feePayer": "4x4Z...", "decimals": 6 } }
  ],
  "signers": {
    "eip155:*": ["0x1892f72fdB3A966b2AD8595aA5f7741Ef72d6085"],
    "solana:*": ["4x4ZhcqiT1FnirM8Ne97iVupkN4NcQgc2YYbE2jDZbZn"]
  }
}

POST /verify

Verifies a payment signature without settling on-chain.

response
{ "success": true, "verified": true }

POST /settle

Verifies and executes the payment on-chain. Returns the transaction hash.

response
{ "success": true, "txHash": "0x123...", "blockNumber": 12345678 }

GET /discovery/resources

Returns a catalog of discovered x402 resources (Bazaar).

request
GET /discovery/resources?type=http&limit=20&offset=0

GET /activity · /live-settlements · /leaderboard

Analytics endpoints — ecosystem visibility based on successful settle events.

examples
GET /activity?window=24h
GET /live-settlements?limit=20
GET /leaderboard?window=24h&limit=50

Zauth Protection

Trust infrastructure for x402

Validates target endpoints before payment is processed — protecting users from paying for broken or malicious APIs.

Pre-Payment Validation

Validates endpoints with HEAD/GET before allowing payment. If down, payment is blocked.

Payment Protection

If validation fails, returns 402 with error details — no funds charged.

Smart Validation

Uses HEAD for GET endpoints (lighter), full method for POST/PUT with headers and body.

Telemetry & Monitoring

Tracks endpoint health, validation results, and payment protection statistics.

How Zauth works

1Intercepts all x402 payment requests before processing
2Validates target URL with same method, headers, and body
3Allows payment if validation passes
4Blocks with 402 error if validation fails — no charge
Zauth error response
{
  "error": "Target endpoint validation failed",
  "status": 404,
  "message": "Endpoint returned error before payment — payment blocked",
  "accepts": [{ "scheme": "exact", "description": "Endpoint validation failed (404) - payment blocked" }]
}
SDK referencex402 ProtocolNetworks