x402-facilitator

SBC x402 Facilitator — verifies and settles payments using the x402 protocol (v2).

Uses ERC-2612 Permit for EVM chains (SBC token doesn't support EIP-3009) and delegated SPL transfers for Solana. The facilitator never holds customer funds.

x402 v2 Compatibility → — 36/36 checks passing | Observability →

Supported Networks

Network	CAIP-2 ID	Env Prefix	Mechanism
Base	eip155:8453	BASE_	ERC-2612 Permit + TransferFrom
Base Sepolia	eip155:84532	BASE_SEPOLIA_	ERC-2612 Permit + TransferFrom
Radius	eip155:723487	RADIUS_	ERC-2612 Permit + TransferFrom
Radius Testnet	eip155:72344	RADIUS_TESTNET_	ERC-2612 Permit + TransferFrom
Solana	solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp	SOLANA_	Delegated SPL token transfer

Each network has its own env vars — mainnets and testnets can be configured simultaneously.

Setup

npm install
cp .env.example .env  # configure facilitator keys per network

Concurrency & Settlement Safety

• Per-EOA settlement queue — On-chain execution is serialized per facilitator wallet to prevent nonce collisions. Critical for chains without a mempool (e.g. Radius) where concurrent nonce submissions fail immediately. Different chains settle in parallel since they use separate wallets.
• Idempotent settle — If a permit nonce was already settled, /settle returns the original { success: true, transaction: "0x..." } instead of failing. Enables safe retries when HTTP responses are lost.
• Partial tx hash on failure — If permit() succeeds but transferFrom() fails, the permit tx hash is included in the error response for on-chain debugging.

Authentication

The facilitator is permissionless — no API key needed. Rate limiting is applied to payment endpoints.

API Endpoints

Method	Path	Description
GET	/supported	Capability discovery — returns kinds, extensions, signers
POST	/verify	Verify a paymentPayload (v2 JSON object)
POST	/settle	Execute on-chain settlement
GET	/health	Health check

v2 Request Format

/verify and /settle accept:

{
  "paymentPayload": {
    "x402Version": 2,
    "resource": "https://...",
    "accepted": { "scheme": "exact", "network": "eip155:8453" },
    "payload": {
      "signature": "0x...",
      "authorization": {
        "from": "0x...",
        "to": "0x...",
        "value": "10000",
        "validAfter": "0",
        "validBefore": "1700000000",
        "nonce": "0"
      }
    },
    "extensions": {}
  },
  "paymentRequirements": {
    "scheme": "exact",
    "network": "eip155:8453",
    "maxAmountRequired": "10000",
    "asset": "0x...",
    "payTo": "0x...",
    "maxTimeoutSeconds": 60,
    "extra": { "assetTransferMethod": "erc2612", "name": "Stable Coin", "version": "1" }
  }
}

Configuration

All config via .env — see .env.example. Each network is independent: only networks with a FACILITATOR_PRIVATE_KEY and FACILITATOR_ADDRESS set will appear in /supported.

The server auto-selects the next available port if FACILITATOR_PORT (default 3001) is in use.

Demo

Interactive demo using SBC tokens. Generates wallets, checks balances, approves the facilitator, then sends a v2 verify + settle request.

npm run setup -- --network <name>   # generate wallets, approve, write .env
npm run dev                          # start server (Terminal 1)
npm run demo -- --network <name>    # run demo client (Terminal 2)

Networks: base (default), base-sepolia, radius, radius-testnet

If the server landed on a different port (e.g. 3002), pass it to the demo:

FACILITATOR_PORT=3002 npm run demo -- --network radius-testnet

To run against a deployed facilitator instead of a local server:

FACILITATOR_URL=https://x402.stablecoin.xyz npm run demo -- --network radius-testnet

The demo client signs an ERC-2612 Permit off-chain (no gas), then the facilitator calls permit() + transferFrom() on-chain to move SBC from Client → Merchant. The client wallet needs SBC; the facilitator only needs ETH for gas.

Observability

Structured JSON logging (Pino) with request correlation via X-Request-ID header. Prometheus metrics on /metrics.

Logs

Logs ship to Grafana Cloud Loki via sbc-log-shipper. Locally:

npm run dev | npx pino-pretty

Set LOG_LEVEL env var to control verbosity (debug, info, warn, error). Default: info.

Metrics

/metrics exposes Prometheus metrics, protected by METRICS_TOKEN env var (bearer auth). Returns 404 if unset.

Metric	Type	Labels
x402_verify_total	Counter	network, result (valid/invalid/bad_request/rpc_error/unknown)
x402_settle_total	Counter	network, result (success/failed/replay/expired/bad_request/insufficient_allowance/nonce_conflict/gas_error/invalid_signature/tx_reverted/rpc_error/receipt_timeout/unknown)
x402_verify_duration_seconds	Histogram	network
x402_settle_duration_seconds	Histogram	network
Default process metrics	—	CPU, memory, event loop lag

# Local test
METRICS_TOKEN=test npm run dev
curl localhost:3001/metrics -H "Authorization: Bearer test"

Grafana Cloud

• Stack: sbclogs.grafana.net
• Loki (logs): query with {app="sbc-x402-facilitator"} | json
• Prometheus (metrics): scraped by sbc-grafana-alloy → remote-write to Grafana Cloud

Example LogQL queries:

# All settle errors on Base
{app="sbc-x402-facilitator"} | json | action="settle" | level="error" | network="eip155:8453"

# Trace a request
{app="sbc-x402-facilitator"} | json | requestId="<uuid>"

Example PromQL queries:

# Settle success rate (5m window)
sum(rate(x402_settle_total{result="success"}[5m])) / sum(rate(x402_settle_total[5m]))

# Verify latency p95
histogram_quantile(0.95, rate(x402_verify_duration_seconds_bucket[5m]))

# Settle errors by network
sum by (network) (rate(x402_settle_total{result!="success"}[5m]))

Alert rules (Grafana)

See grafana/alerts.yaml for full PromQL expressions.

Alert	Condition
Settle failure rate high	Non-success rate > 10% over 5min
RPC errors spiking	3+ RPC failures in 5min
Nonce conflicts detected	Any nonce collision
Permit expired attempts	Any expired permit settle
Signature errors spiking	3+ invalid signatures in 5min
Health down	No facilitator logs for 10min

Development

npm run dev           # watch mode (auto-restart)
npm test              # run tests (187 tests)
npm run build         # compile TypeScript
npm start             # production
fly deploy            # deploy to Fly.io