x402 Facilitator

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Base URL

https://facilitator.x84.ai

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How it works

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Endpoints

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x84 extensions

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Supported assets

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Verification rules

1. Deserialization — Transaction must be a valid Solana VersionedTransaction
2. Allowed programs — Only SPL Token, ComputeBudget, and Memo programs are permitted
3. Transfer instruction — Must contain exactly one TransferChecked instruction
4. Amount match — Transfer amount must match the payment requirements
5. Mint match — Token mint must match the required asset
6. Destination match — Transfer destination must match the payTo address
7. Fee payer — Must be the facilitator’s public key (from /supported signers)
8. Replay prevention — Already-signed transactions are rejected

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Idempotency

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v1 backward compatibility

• v2 (recommended) — Structured PaymentPayload object with x402Version, accepted, payload, and optional extensions
• v1 (legacy) — Base64-encoded JSON string, automatically normalized to v2 internally

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Integration example

import { X84A2AClient } from "@x84/sdk";

const client = new X84A2AClient({
  wallet: myKeypair,
  rpcUrl: "https://api.devnet.solana.com",
  facilitatorUrl: "https://facilitator.x84.ai",
});

// The SDK handles the full x402 flow automatically:
// 1. Sends request → gets 402 → builds tx → calls /settle → retries with proof
const result = await client.sendMessage(agentUrl, {
  message: { role: "user", parts: [{ type: "text", text: "Hello" }] },
});