AnySpend facilitator

Payment processor for x402 multi-token payments

GitHub Repository

View source code, examples, and contribute

npm Package

Install @b3dotfun/anyspend-x402 package

Overview

The AnySpend x402 Facilitator handles multi-token, cross-chain payments for the x402 protocol. It takes care of token swaps, cross-chain bridging, and settlement so developers can accept payments in any token while receiving their preferred currency.

Production Endpoint: https://mainnet.anyspend.com/x402

Key capabilities

Multi-token payment processing

Accept payments in any ERC-20 token that supports EIP-2612 (permit) or EIP-3009 (transferWithAuthorization):

Stablecoins: USDC, USDT (on supported chains)
Native tokens: ETH, SOL, BNB, MATIC
Custom tokens: Any token with permit support, including project tokens like B3
19+ Networks: Support across EVM chains (Base, Ethereum, Arbitrum, etc.) and SVM (Solana)

Cross-chain routing

Automatically handles payments across different blockchain networks:

Same-chain payments: Direct token transfers with minimal overhead
Cross-chain payments: Automatic bridging between networks (e.g., ETH → Base)
Cross-VM payments: Experimental support for Solana ↔ EVM transfers
Optimal routing: Smart route selection for best execution

Automatic token conversion

Converts between any supported tokens:

Buyer flexibility: Users pay with whatever token they hold
Seller preference: Merchants receive their chosen settlement currency
Best pricing: Routes through optimal DEX liquidity sources
Slippage protection: Automatic safeguards against price impact

Gasless payments

Users never pay gas fees:

Facilitator covers all on-chain gas costs
Users only sign EIP-712 messages
No need to hold native tokens for gas
Smooth user experience across all chains

Standards compliance

x402 protocol compliant

The AnySpend Facilitator implements the complete x402 specification:

HTTP-native payments via 402 Payment Required status
Standard headers (X-PAYMENT, X-PAYMENT-RESPONSE, X-PREFERRED-TOKEN)
Exact payment scheme with recipient and amount verification
Signature-based authorization (EIP-712, EIP-2612, EIP-3009)
Cryptographic verification without trusted third parties

Drop-in replacement

Fully compatible with any x402 implementation:

Client compatibility: Works with any x402-compliant client
Server compatibility: Can be used with any x402 middleware
No vendor lock-in: Standard HTTP APIs, switch facilitators anytime
Interoperability: Integrates with Coinbase CDP x402, PayAI, and others

Architecture

Payment flow

text
┌──────────────┐
│    Client    │  Signs payment authorization
│  (Any Token) │  preferredToken: USDT
└──────┬───────┘
       │
       │ X-PAYMENT header
       ▼
┌──────────────────────────┐
│   Resource Server        │
│   (Your API)             │
│                          │
│  AnySpend Middleware     │
│  • Intercepts request    │
│  • Gets quote            │
│  • Returns 402           │
└──────┬───────────────────┘
       │
       │ /verify, /settle
       ▼
┌──────────────────────────┐
│  AnySpend Facilitator    │
│  mainnet.anyspend.com    │
│                          │
│  • Validates signature   │
│  • Executes token swap   │
│  • Settles to seller     │
└──────┬───────────────────┘
       │
       │ On-chain txs
       ▼
┌──────────────────────────┐
│      Blockchain          │
│  • Receive payment       │
│  • Swap tokens (if needed) │
│  • Settle to merchant    │
└──────────────────────────┘

Infrastructure components

API Layer

RESTful HTTP API for payment verification and settlement
WebSocket support for real-time payment status updates
Rate limiting and DDoS protection
99.9% uptime SLA

Swap Engine

Aggregates liquidity from multiple DEXs
Optimal routing for best execution prices
Slippage protection and MEV resistance
Cross-chain bridging integration

Settlement System

Parallel transaction processing
Automatic nonce management
Failed transaction recovery
Real-time settlement confirmation

Security

EIP-712 signature verification
Replay attack prevention (nonce tracking)
Deadline enforcement
Smart contract audits

API endpoints

POST /verify

Validates payment signature without executing on-chain.

Purpose:

Fast validation (under 100ms)
Check signature authenticity
Verify deadline hasn't expired
No gas costs

Request:

json
{
  "x402Version": "0.2",
  "paymentHeader": "base64_encoded_payment",
  "paymentRequirements": {
    "scheme": "exact",
    "network": "base-mainnet",
    "amount": "1000000",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "recipient": "0xMerchantAddress..."
  }
}

Response:

json
{
  "valid": true
}

POST /settle

Executes on-chain settlement and returns transaction proof.

Purpose:

Execute payment authorization
Swap tokens if needed (buyer token → seller token)
Settle to resource server
Return transaction hash for verification

Request:

json
{
  "x402Version": "0.2",
  "paymentHeader": "base64_encoded_payment",
  "paymentRequirements": { /* ... */ }
}

Response:

json
{
  "txHash": "0xabc123...",
  "network": "base-mainnet",
  "metadata": {
    "receiptTxHash": "0x...",
    "swapTxHash": "0x...",
    "settlementTxHash": "0x..."
  }
}

POST /quote

Get token conversion rate for multi-token payments.

Purpose:

Calculate exact token amount for payment
Get current exchange rate
Estimate swap execution time

Request:

json
{
  "usdcAmount": "1000000",        // Target amount (1 USDC)
  "paymentToken": "0xfde4...",    // USDT address
  "network": "base-mainnet"
}

Response:

json
{
  "tokenAmount": "1000000",  // 1.0 USDT needed
  "exchangeRate": "1.0",
  "deadline": 1730000000,
  "route": {
    "srcToken": "0xfde4...",
    "dstToken": "0x8335...",
    "path": ["USDT", "USDC"]
  }
}

GET /supported

Lists supported payment schemes and networks.

Response:

json
{
  "schemes": [{
    "scheme": "exact",
    "networks": [
      "base",
      "ethereum",
      "arbitrum",
      "optimism",
      "polygon",
      "bsc",
      "avalanche",
      "solana"
    ]
  }]
}

Integration

Server-Side (Express)

typescript
import { paymentMiddleware, facilitator } from '@b3dotfun/anyspend-x402';

const endpointConfig = {
  '/api/premium': {
    amount: '1.00',
    asset: 'USD'
  }
};

app.use(paymentMiddleware(
  '0xYourAddress...',
  endpointConfig,
  facilitator  // Pre-configured to mainnet.anyspend.com/x402
));

Server-Side (Custom)

typescript
import { X402Facilitator } from '@b3dotfun/anyspend-x402';

const facilitator = new X402Facilitator({
  url: 'https://mainnet.anyspend.com/x402',
  apiKey: process.env.ANYSPEND_API_KEY  // Optional
});

// Verify payment
const { valid } = await facilitator.verify(paymentHeader, requirements);

// Settle payment
const { txHash } = await facilitator.settle(paymentHeader, requirements);

Client-Side

typescript
import { X402Client } from 'anyspend-x402-client';

const client = new X402Client({
  walletClient,
  facilitatorUrl: 'https://mainnet.anyspend.com/x402'  // Optional, uses this by default
});

const response = await client.request('https://api.example.com/premium');