RelAI SDK Now Supports WebSocket Relay - Here’s How to Use It

Starting now, RelAI SDK includes built-in WebSocket relay transport for x402 payments.

That means you can keep the same client.fetch(...) integration, but unlock faster real-time paid flows for interactive apps and AI agents. And yes - HTTP fallback is still available when needed.

This is one of the biggest transport UX upgrades in the SDK so far, and adoption is literally a small config change.

In this post, you get copy-paste examples for:

1. Minimal SDK setup
2. Standard relay calls
3. WebSocket relay transport
4. Whitelabel URL support
5. React hook usage

1) Install

npm install @relai-fi/x402

2) Create client once

import { createX402Client } from '@relai-fi/x402';
const client = createX402Client({
  wallets: {
    // Solana wallet (required for Solana payments)
    solana: {
      publicKey: solanaWallet.publicKey,
      signTransaction: solanaWallet.signTransaction,
    },
    // EVM wallet (required for EVM payments)
    evm: {
      address: evmWallet.address,
      signTypedData: evmWallet.signTypedData,
    },
  },
  facilitatorUrl: 'https://facilitator.x402.fi',
  relayWs: {
    enabled: true,
    // Optional explicit relay WS endpoint
    wsUrl: 'wss://api.relai.fi/api/ws/relay',
  },
  verbose: true,
});

3) Basic paid relay call

Use your normal relay HTTP URL. The SDK handles 402 automatically.

const response = await client.fetch(
  'https://api.relai.fi/relay/1765103787374/projects?page=1',
  { method: 'GET' }
);
const data = await response.json();
console.log(data);

4) WebSocket relay transport (same fetch API)

You still call client.fetch(...). With relayWs.enabled=true, SDK can run the preflight + paid retry flow over WS.

const client = createX402Client({
  wallets,
  relayWs: {
    enabled: true,
    wsUrl: 'wss://api.relai.fi/api/ws/relay',
    fallbackToHttp: true,
  },
});
const response = await client.fetch(
  'https://api.relai.fi/relay/1765103787374/v1/chat/completions',
  {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      messages: [{ role: 'user', content: 'Hello from WS transport' }],
    }),
  }
);

5) Whitelabel URL example

RelAI SDK also supports whitelabel URLs directly.

const response = await client.fetch('https://myapi.x402.fi/projects?page=1', {
  method: 'GET',
});
const data = await response.json();

This allows buyers to use branded hostnames while keeping the same payment flow.

6) React hook example (useRelaiPayment)

import { useRelaiPayment } from '@relai-fi/x402/react';
export function PayButton() {
  const { fetch, isLoading, transactionUrl } = useRelaiPayment({
    wallets: {
      solana: solanaWallet,
      evm: evmWallet,
    },
    relayWs: {
      enabled: true,
      wsUrl: 'wss://api.relai.fi/api/ws/relay',
    },
  });
const onClick = async () => {
    const res = await fetch('https://myapi.x402.fi/projects?page=1', {
      method: 'GET',
    });
    console.log(await res.json());
  };
return (
    
      {isLoading ? 'Paying...' : 'Pay and Fetch'}
    
  );
}

8) Quick production tips

• Keep a single SDK client instance per session.
• Enable verbose: true while integrating, then disable in production.
• Do not hardcode private keys or secrets in frontend code.
• Keep HTTP fallback enabled unless you explicitly want WS-only behavior.