x402 Quickstart - XentFi API Documentation

Prerequisites

A XentFi account with a WAAS apiKey and orgId (dashboard.xentfi.com — see Authentication)
Node.js 20+
viem if you’ll be signing payments as a payer (installed automatically as a dependency)

Step 1: Install

npm install @xentfi/x402-facilitator

Step 2: Set your environment variables

export WAAS_API_KEY="your-waas-api-key"
export WAAS_ORG_ID="your-waas-org-id"

Step 3: Construct the client and check supported configurations

import { X402FacilitatorClient } from "@xentfi/x402-facilitator";

const facilitator = new X402FacilitatorClient({
  apiKey: process.env.WAAS_API_KEY!,
  orgId: process.env.WAAS_ORG_ID!,
});

const supported = await facilitator.getSupported();
console.log(supported);

Example response

{
  "protocolVersion": "1.0.0",
  "facilitatorAddress": "0xa639b98096c4293e507727a296cb6cb862a9ca8d",
  "supportedConfigurations": [
    {
      "network": { "id": "base-mainnet", "name": "Base", "type": "mainnet" },
      "gasSponsorship": { "enabled": true, "maxSponsorshipValueUsd": "5.00" },
      "tokens": [
        {
          "id": "asset_usdc",
          "name": "USD Coin",
          "symbol": "USDC",
          "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
          "decimals": 6,
          "version": "2",
          "supportedSchemes": [{ "type": "eip3009", "methods": ["transferWithAuthorization"] }]
        }
      ]
    }
  ]
}

getSupported() requires no authentication and is the fastest way to confirm the SDK is wired up correctly and to discover valid blockchainId/assetId pairs and token domain parameters for signing.

The facilitator URL (https://api.xentfi.com/v1/x402) and relayer wallet are fixed on the backend — they are not configurable in the client. apiKey and orgId are the only two options X402FacilitatorClient takes.

Next: pick your role

I'm getting paid

Set up verify() + settle() on a resource server.

I'm making a payment

Sign an EIP-3009 authorization and attach it as X-PAYMENT.