Agent Public Payment — Local-Signed Payment Workflow

{
  "name": "agent_public_payment",
  "description": "Complete end-to-end X402 cross-chain payment automation for AI agents using AgentTech SDK in public mode. Generates wallets locally, creates intents, signs X402 proofs locally, submits proofs, and polls for completion. No API key required, full control over private keys.",
  "input_schema": {
    "type": "object",
    "properties": {
      "recipient": {
        "type": "string",
        "description": "Recipient wallet address (Base 0x address) or email address"
      },
      "email": {
        "type": "string",
        "description": "Recipient email address (alternative to recipient)"
      },
      "amount": {
        "type": "string",
        "description": "USD amount as string (e.g. '10.50'). Minimum: 0.01, Maximum: 1,000,000. Up to 6 decimal places."
      },
      "payer_chain": {
        "type": "string",
        "description": "Source chain identifier. See Supported Chains documentation for the full list of supported chains."
      },
      "wallet_type": {
        "type": "string",
        "enum": ["evm", "solana"],
        "description": "Type of wallet to use for signing (must match payer_chain)"
      }
    },
    "required": ["amount", "payer_chain", "wallet_type"],
    "oneOf": [
      { "required": ["email"] },
      { "required": ["recipient"] }
    ]
  },
  "output_schema": {
    "type": "object",
    "properties": {
      "intent_id": {
        "type": "string",
        "description": "Unique identifier for the created intent"
      },
      "status": {
        "type": "string",
        "enum": ["TARGET_SETTLED", "EXPIRED", "VERIFICATION_FAILED", "PARTIAL_SETTLEMENT"],
        "description": "Final status of the payment"
      },
      "transaction_hash": {
        "type": "string",
        "description": "Transaction hash on the target chain (available when status is TARGET_SETTLED)"
      },
      "payer_wallet": {
        "type": "object",
        "description": "Generated wallet information"
      }
    },
    "required": ["intent_id", "status"]
  }
}

import { PublicPayClient } from '@cross402/usdc';
import { Wallet } from 'ethers';
import { buildEVMsettleProof } from './x402-signing';

async function completeX402Payment(recipient: string, amount: string) {
  // Step 1: Generate or load wallet
  const wallet = Wallet.createRandom();
  const payerAddress = wallet.address;
  const privateKey = wallet.privateKey;

  // Step 2: Initialize SDK client
  const client = new PublicPayClient({
    baseUrl: 'https://api-pay.agent.tech',
  });

  // Step 3: Create intent — payer on Base, merchant paid on Ethereum.
  const intent = await client.createIntent({
    recipient,
    amount,
    payerChain: 'base',
    targetChain: 'ethereum',
  });

  console.log(`Intent created: ${intent.intentId}`);
  console.log(`Payment requirements:`, intent.paymentRequirements);

  // Step 4: Sign X402 proof locally
  const settleProof = buildEVMsettleProof(
    intent.paymentRequirements,
    payerAddress,
    privateKey
  );

  // Step 5: Submit proof
  const result = await client.submitProof(intent.intentId, settleProof);
  console.log(`Proof submitted. Status: ${result.status}`);

  // Step 6: Poll until completion
  let finalIntent = result;
  while (
    finalIntent.status !== 'TARGET_SETTLED' &&
    finalIntent.status !== 'PARTIAL_SETTLEMENT' &&
    finalIntent.status !== 'EXPIRED' &&
    finalIntent.status !== 'VERIFICATION_FAILED'
  ) {
    await new Promise(resolve => setTimeout(resolve, 3000));
    finalIntent = await client.getIntent(intent.intentId);
    console.log(`Status: ${finalIntent.status}`);
  }

  if (finalIntent.status === 'TARGET_SETTLED') {
    console.log(`Payment complete! Transaction: ${finalIntent.targetPayment.txHash}`);
    return {
      success: true,
      intentId: finalIntent.intentId,
      txHash: finalIntent.targetPayment.txHash,
    };
  } else {
    throw new Error(`Payment failed: ${finalIntent.status}`);
  }
}

npm install ethers

import { Wallet } from 'ethers';

const wallet = Wallet.createRandom();
const evmWallet = {
  type: 'evm',
  symbol: 'ETH',
  address: wallet.address,
  private_key: wallet.privateKey,
  mnemonic: wallet.mnemonic?.phrase,
};

console.log(`EVM Address: ${wallet.address}`);
console.log(`Private Key: ${wallet.privateKey}`);

package main

import (
    "crypto/ecdsa"
    "fmt"
    "github.com/ethereum/go-ethereum/accounts"
    "github.com/ethereum/go-ethereum/crypto"
)

func generateEVMWallet() (string, string, error) {
    privateKey, err := crypto.GenerateKey()
    if err != nil {
        return "", "", err
    }
    
    publicKey := privateKey.Public()
    publicKeyECDSA, ok := publicKey.(*ecdsa.PublicKey)
    if !ok {
        return "", "", fmt.Errorf("error casting public key")
    }
    
    address := crypto.PubkeyToAddress(*publicKeyECDSA).Hex()
    privateKeyHex := fmt.Sprintf("%x", crypto.FromECDSA(privateKey))
    
    return address, privateKeyHex, nil
}

npm install @solana/web3.js

import { Keypair } from '@solana/web3.js';
import * as bs58 from 'bs58';

const keypair = Keypair.generate();
const solWallet = {
  type: 'solana',
  symbol: 'SOL',
  address: keypair.publicKey.toBase58(),
  private_key: bs58.encode(keypair.secretKey),
};

console.log(`Solana Address: ${keypair.publicKey.toBase58()}`);

package main

import (
    "encoding/base64"
    "fmt"
    "github.com/gagliardetto/solana-go"
)

func generateSolanaWallet() (string, string, error) {
    keypair := solana.NewWallet()
    address := keypair.PublicKey().String()
    privateKey := base64.StdEncoding.EncodeToString(keypair.PrivateKey)
    
    return address, privateKey, nil
}

import * as fs from 'fs';
import * as path from 'path';
import * as os from 'os';

function saveWallets(evmWallet: any, solWallet: any) {
  const walletsData = {
    created_at: new Date().toISOString(),
    wallets: [evmWallet, solWallet],
  };
  
  const configDir = path.join(os.homedir(), '.config', 'x402pay');
  fs.mkdirSync(configDir, { recursive: true });
  
  const filePath = path.join(configDir, 'wallets.json');
  fs.writeFileSync(filePath, JSON.stringify(walletsData, null, 2));
  
  console.log(`Wallets saved to ${filePath}`);
}

package main

import (
    "encoding/json"
    "os"
    "path/filepath"
    "time"
)

type WalletData struct {
    CreatedAt string   `json:"created_at"`
    Wallets   []Wallet `json:"wallets"`
}

func saveWallets(evmWallet, solWallet Wallet) error {
    walletsData := WalletData{
        CreatedAt: time.Now().UTC().Format(time.RFC3339),
        Wallets:   []Wallet{evmWallet, solWallet},
    }
    
    configDir := filepath.Join(os.Getenv("HOME"), ".config", "x402pay")
    os.MkdirAll(configDir, 0755)
    
    filePath := filepath.Join(configDir, "wallets.json")
    data, err := json.MarshalIndent(walletsData, "", "  ")
    if err != nil {
        return err
    }
    
    return os.WriteFile(filePath, data, 0600)
}

function chooseSigningMethod(paymentRequirements: PaymentRequirements): string {
  const network = paymentRequirements.network;

  // Solana chains
  if (network.startsWith('solana:')) {
    return 'solana';
  }

  // EVM chains — the Permit2 + EIP-2612 path is opt-in per chain
  if (paymentRequirements.extra?.assetTransferMethod === 'permit2') {
    return 'permit2';
  }

  return 'eip3009';
}

import { Wallet } from 'ethers';
import * as crypto from 'crypto';

interface PaymentRequirements {
  scheme: string;
  network: string;
  amount: string;
  asset: string;
  payTo: string;
  maxTimeoutSeconds: number;
  resource?: string;
  description?: string;
  extra?: {
    name?: string;
    version?: string;
    assetTransferMethod?: 'permit2';  // present on chains that require Permit2 + EIP-2612
    feePayer?: string;                // Solana: fee payer public key
    decimals?: number;                // Solana: token decimals
  };
}

function buildEVMsettleProof(
  paymentRequirements: PaymentRequirements,
  payerAddress: string,
  privateKey: string
): string {
  // Parse chainId from CAIP-2 (eip155:8453 -> 8453)
  const network = paymentRequirements.network;
  const chainIdMatch = network.match(/eip155:(\d+)/);
  if (!chainIdMatch) {
    throw new Error(`Invalid network format: ${network}`);
  }
  const chainId = parseInt(chainIdMatch[1], 10);

  const amount = paymentRequirements.amount;
  const payTo = paymentRequirements.payTo;
  const asset = paymentRequirements.asset;
  const extra = paymentRequirements.extra || {};
  const name = extra.name || 'USD Coin';
  const version = extra.version || '2';
  const maxTimeout = paymentRequirements.maxTimeoutSeconds || 600;

  // Generate nonce
  const nonce = '0x' + crypto.randomBytes(32).toString('hex');
  
  // Set validity window
  const now = Math.floor(Date.now() / 1000);
  const validAfter = (now - 600).toString();
  const validBefore = (now + maxTimeout).toString();

  // Build EIP-712 domain
  const domain = {
    name,
    version,
    chainId,
    verifyingContract: asset,
  };

  // Build EIP-712 types
  const types = {
    TransferWithAuthorization: [
      { name: 'from', type: 'address' },
      { name: 'to', type: 'address' },
      { name: 'value', type: 'uint256' },
      { name: 'validAfter', type: 'uint256' },
      { name: 'validBefore', type: 'uint256' },
      { name: 'nonce', type: 'bytes32' },
    ],
  };

  // Build message
  const message = {
    from: payerAddress,
    to: payTo,
    value: amount,
    validAfter,
    validBefore,
    nonce,
  };

  // Sign with ethers
  const wallet = new Wallet(privateKey);
  const signature = wallet.signTypedData(domain, types, message);

  // Build X402 v2 payload
  const payload = {
    x402Version: 2,
    resource: {
      url: paymentRequirements.resource || '/api/intents',
      description: paymentRequirements.description || 'X402 payment',
      mimeType: 'application/json',
    },
    accepted: {
      scheme: paymentRequirements.scheme || 'exact',
      network,
      amount,
      asset,
      payTo,
      maxTimeoutSeconds: maxTimeout,
      extra: paymentRequirements.extra || {},
    },
    payload: {
      signature: signature,
      authorization: {
        from: payerAddress,
        to: payTo,
        value: amount,
        validAfter,
        validBefore,
        nonce,
      },
    },
  };

  // Encode as base64
  return Buffer.from(JSON.stringify(payload)).toString('base64');
}

const PERMIT2_ADDRESS = '0x000000000022D473030F116dDEE9F6B43aC78BA3';
const X402_EXACT_PERMIT2_PROXY = '0x402085c248EeA27D92E8b30b2C58ed07f9E20001';

import { Wallet, Contract } from 'ethers';
import * as crypto from 'crypto';

function randomNonce256Hex(): string {
  return '0x' + crypto.randomBytes(32).toString('hex');
}

function randomNonce256Decimal(): string {
  const bytes = crypto.randomBytes(32);
  let value = 0n;
  for (const b of bytes) {
    value = (value << 8n) | BigInt(b);
  }
  return value.toString();
}

async function buildPermit2SettleProof(
  paymentRequirements: PaymentRequirements,
  payerAddress: string,
  privateKey: string,
  rpcUrl: string
): Promise<string> {
  // Parse chainId from CAIP-2 (eip155:42161 -> 42161)
  const network = paymentRequirements.network;
  const chainIdMatch = network.match(/eip155:(\d+)/);
  if (!chainIdMatch) {
    throw new Error(`Invalid network format: ${network}`);
  }
  const chainId = parseInt(chainIdMatch[1], 10);

  const amount = paymentRequirements.amount;
  const payTo = paymentRequirements.payTo;
  const asset = paymentRequirements.asset;
  const extra = paymentRequirements.extra || {};
  const maxTimeout = paymentRequirements.maxTimeoutSeconds || 600;

  const now = Math.floor(Date.now() / 1000);
  const validAfter = (now - 600).toString();
  const deadline = (now + maxTimeout).toString();

  const wallet = new Wallet(privateKey);

  // --- Signature 1: Permit2 PermitWitnessTransferFrom ---
  const permit2Nonce = randomNonce256Decimal();
  const permit2Domain = {
    name: 'Permit2',
    chainId: chainId,
    verifyingContract: PERMIT2_ADDRESS,
  };
  const permit2Types = {
    PermitWitnessTransferFrom: [
      { name: 'permitted', type: 'TokenPermissions' },
      { name: 'spender', type: 'address' },
      { name: 'nonce', type: 'uint256' },
      { name: 'deadline', type: 'uint256' },
      { name: 'witness', type: 'Witness' },
    ],
    TokenPermissions: [
      { name: 'token', type: 'address' },
      { name: 'amount', type: 'uint256' },
    ],
    Witness: [
      { name: 'to', type: 'address' },
      { name: 'validAfter', type: 'uint256' },
    ],
  };
  const permit2Message = {
    permitted: { token: asset, amount },
    spender: X402_EXACT_PERMIT2_PROXY,
    nonce: permit2Nonce,
    deadline,
    witness: { to: payTo, validAfter },
  };

  const permit2Signature = await wallet.signTypedData(
    permit2Domain,
    permit2Types,
    permit2Message
  );

  // --- Signature 2: EIP-2612 Permit (approve Permit2 to spend tokens) ---
  // Read current nonce from USDC contract
  const { JsonRpcProvider } = await import('ethers');
  const provider = new JsonRpcProvider(rpcUrl);
  const usdcContract = new Contract(
    asset,
    ['function nonces(address owner) view returns (uint256)'],
    provider
  );
  const eip2612Nonce = await usdcContract.nonces(payerAddress);

  const permitDomain = {
    name: extra.name || 'USD Coin',
    version: extra.version || '2',
    chainId,
    verifyingContract: asset,
  };
  const permitTypes = {
    Permit: [
      { name: 'owner', type: 'address' },
      { name: 'spender', type: 'address' },
      { name: 'value', type: 'uint256' },
      { name: 'nonce', type: 'uint256' },
      { name: 'deadline', type: 'uint256' },
    ],
  };
  const permitMessage = {
    owner: payerAddress,
    spender: PERMIT2_ADDRESS,
    value: amount,
    nonce: eip2612Nonce.toString(),
    deadline,
  };

  const permitSignature = await wallet.signTypedData(
    permitDomain,
    permitTypes,
    permitMessage
  );

  // --- Build X402 v2 payload with extensions ---
  const payload = {
    x402Version: 2,
    resource: {
      url: paymentRequirements.resource || '/api/intents',
      description: paymentRequirements.description || 'X402 payment',
      mimeType: 'application/json',
    },
    accepted: {
      scheme: paymentRequirements.scheme || 'exact',
      network,
      amount,
      asset,
      payTo,
      maxTimeoutSeconds: maxTimeout,
      extra: paymentRequirements.extra || {},
    },
    payload: {
      signature: permit2Signature,
      permit2Authorization: {
        permitted: { token: asset, amount },
        from: payerAddress,
        spender: X402_EXACT_PERMIT2_PROXY,
        nonce: permit2Nonce,
        deadline,
        witness: { to: payTo, validAfter },
      },
    },
    extensions: {
      eip2612GasSponsoring: {
        info: {
          from: payerAddress,
          asset,
          spender: PERMIT2_ADDRESS,
          amount,
          nonce: eip2612Nonce.toString(),
          deadline,
          signature: permitSignature,
          version: '1',
        },
      },
    },
  };

  return Buffer.from(JSON.stringify(payload)).toString('base64');
}

import {
  Keypair,
  PublicKey,
  TransactionMessage,
  VersionedTransaction,
  SystemProgram,
} from '@solana/web3.js';
import {
  createSetComputeUnitLimitInstruction,
  createSetComputeUnitPriceInstruction,
  createTransferCheckedInstruction,
  getAssociatedTokenAddress,
} from '@solana/spl-token';
import nacl from 'tweetnacl';

interface SolanaPaymentRequirements {
  scheme: string;
  network: string;
  amount: string;
  asset: string;
  payTo: string;
  maxTimeoutSeconds: number;
  extra?: {
    feePayer?: string;
    decimals?: number;
  };
}

async function buildSolanasettleProof(
  paymentRequirements: SolanaPaymentRequirements,
  payerKeypair: Keypair
): Promise<string> {
  const payTo = new PublicKey(paymentRequirements.payTo);
  const asset = new PublicKey(paymentRequirements.asset);
  const amount = BigInt(paymentRequirements.amount);
  const extra = paymentRequirements.extra || {};
  const decimals = extra.decimals || 6;

  // IMPORTANT: feePayer is the server's gas-sponsoring address.
  // The user does NOT have the feePayer's private key.
  // The server will add the feePayer signature after receiving this transaction.
  const feePayer = extra.feePayer ? new PublicKey(extra.feePayer) : payTo;

  // Get associated token address
  const sourceATA = await getAssociatedTokenAddress(asset, payerKeypair.publicKey);
  const destATA = await getAssociatedTokenAddress(asset, payTo);

  // Build instructions
  const instructions = [
    // 1. SetComputeUnitLimit
    createSetComputeUnitLimitInstruction({ units: 200000 }),
    // 2. SetComputeUnitPrice
    createSetComputeUnitPriceInstruction({ microLamports: 1 }),
    // 3. TransferChecked
    createTransferCheckedInstruction(
      sourceATA,
      asset,
      destATA,
      payerKeypair.publicKey,
      amount,
      decimals
    ),
  ];

  // Build transaction message
  const messageV0 = new TransactionMessage({
    payerKey: feePayer,
    recentBlockhash: '11111111111111111111111111111111', // Will be replaced by backend
    instructions,
  }).compileToV0Message();

  // Create versioned transaction
  const transaction = new VersionedTransaction(messageV0);

  // CRITICAL: Use partial sign — only sign with YOUR keypair.
  // Do NOT use transaction.sign([payerKeypair]) — that would fail because
  // sign() expects ALL signers (including feePayer) to be provided.
  // The feePayer is the server's address; we don't have its private key.
  // addSignature() lets us sign only our part, leaving the feePayer's
  // signature slot as zero bytes for the server to fill in later.
  transaction.addSignature(payerKeypair.publicKey,
    nacl.sign.detached(transaction.message.serialize(), payerKeypair.secretKey)
  );

  // Serialize and encode
  const transactionBytes = transaction.serialize();
  const transactionBase64 = Buffer.from(transactionBytes).toString('base64');

  // Build X402 v2 payload
  const payload = {
    x402Version: 2,
    resource: {
      url: paymentRequirements.resource || '/api/intents',
      description: paymentRequirements.description || 'X402 payment',
      mimeType: 'application/json',
    },
    accepted: {
      scheme: paymentRequirements.scheme || 'exact',
      network: paymentRequirements.network,
      amount: paymentRequirements.amount,
      asset: paymentRequirements.asset,
      payTo: paymentRequirements.payTo,
      maxTimeoutSeconds: paymentRequirements.maxTimeoutSeconds,
      extra: paymentRequirements.extra || {},
    },
    payload: {
      transaction: transactionBase64,
    },
  };

  // Encode as base64
  return Buffer.from(JSON.stringify(payload)).toString('base64');
}

package main

import (
	"crypto/ed25519"
	"encoding/base64"
	"encoding/json"

	"github.com/gagliardetto/solana-go"
)

// buildSolanaSettleProof constructs a Solana X402 settle proof using partial signing.
//
// CRITICAL CONCEPTS:
//   - feePayer is the SERVER's gas-sponsoring address. You do NOT have its private key.
//   - You must use partial signing: sign only with your own keypair.
//   - The Signatures slice must be pre-allocated with the correct length
//     (one slot per signer in the compiled message). NewTransaction() does NOT
//     do this automatically — you must allocate it yourself.
//   - The feePayer is always index 0 in the Signatures slice. Leave it as
//     zero bytes (64 bytes of 0x00). The server will fill it in.
//   - Your signature goes at the index matching your public key's position
//     in the message's account keys.
func buildSolanaSettleProof(
	paymentRequirements map[string]interface{},
	payerPrivateKey ed25519.PrivateKey,
) (string, error) {
	extra, _ := paymentRequirements["extra"].(map[string]interface{})
	feePayerStr, _ := extra["feePayer"].(string)
	feePayer := solana.MustPublicKeyFromBase58(feePayerStr)
	payTo := solana.MustPublicKeyFromBase58(paymentRequirements["payTo"].(string))
	asset := solana.MustPublicKeyFromBase58(paymentRequirements["asset"].(string))
	_ = payTo
	_ = asset

	// ... (build instructions: SetComputeUnitLimit, SetComputeUnitPrice, TransferChecked)
	// ... (compile to MessageV0 with payerKey = feePayer)

	// After compiling the message to messageBytes:
	var messageBytes []byte // = compiled message bytes

	// Pre-allocate the Signatures slice.
	// The number of required signatures is in messageBytes[0] (the first byte
	// of a Solana v0 message header). Each signature is 64 bytes of zeros initially.
	numSigners := int(messageBytes[0])
	signatures := make([]solana.Signature, numSigners)
	// All slots are initialized to zero bytes — the feePayer slot (index 0)
	// stays as zeros for the server to fill in later.

	// Find YOUR public key's index in the account keys and sign at that index.
	payerPubkey := solana.PublicKeyFromBytes(payerPrivateKey.Public().(ed25519.PublicKey))
	// The feePayer is index 0. Your key will typically be index 1 if you are
	// the second signer. Loop through the message's account keys to find it.
	myIndex := 1 // Typically 1 when feePayer is index 0 and you are the only other signer

	sig := ed25519.Sign(payerPrivateKey, messageBytes)
	copy(signatures[myIndex][:], sig)

	// Serialize: [compact-array of signatures] + [message bytes]
	// Then base64-encode the whole thing for the X402 payload.
	_ = feePayer
	_ = signatures

	// Build X402 v2 payload (same structure as TypeScript example)
	payload := map[string]interface{}{
		"x402Version": 2,
		"payload": map[string]interface{}{
			"transaction": base64.StdEncoding.EncodeToString(messageBytes), // replace with full serialized tx
		},
		// ... include resource, accepted fields
	}

	payloadJSON, err := json.Marshal(payload)
	if err != nil {
		return "", err
	}
	return base64.StdEncoding.EncodeToString(payloadJSON), nil
}

import { PublicPayClient } from '@cross402/usdc';
import { Wallet } from 'ethers';
import { buildEVMsettleProof } from './x402-signing';
import { buildPermit2SettleProof } from './x402-permit2-signing';

async function completeX402PaymentFlow(
  recipient: string,
  amount: string,
  payerChain: string
) {
  // Initialize SDK client (public mode, no auth required)
  const client = new PublicPayClient({
    baseUrl: 'https://api-pay.agent.tech',
  });

  // Step 1: Generate or load wallet
  const wallet = Wallet.createRandom();
  const payerAddress = wallet.address;
  const privateKey = wallet.privateKey;

  console.log(`Using payer wallet: ${payerAddress}`);

  // Step 2: Create intent
  const intent = await client.createIntent({
    recipient,
    amount,
    payerChain,
  });

  console.log(`Intent created: ${intent.intentId}`);
  console.log(`Status: ${intent.status}`);
  console.log(`Expires at: ${intent.expiresAt}`);

  // Step 3: Sign X402 proof locally (choose method based on payment_requirements)
  let settleProof: string;
  const pr = intent.paymentRequirements;

  if (pr.extra?.assetTransferMethod === 'permit2') {
    // Permit2 + EIP-2612 path (BSC/Monad/MegaETH USDC; Polygon USDT/USDT0)
    // When extra.domainType === "salted", buildPermit2SettleProof must use the
    // salted EIP-712 domain for the EIP-2612 Permit (Polygon-PoS layout).
    settleProof = await buildPermit2SettleProof(pr, payerAddress, privateKey, rpcUrl);
  } else {
    // EIP-3009 TransferWithAuthorization path (Base, Ethereum, Polygon USDC, HyperEVM, Arbitrum, SKALE Base)
    settleProof = buildEVMsettleProof(pr, payerAddress, privateKey);
  }

  console.log('X402 proof signed locally');

  // Step 4: Submit proof
  const submitResult = await client.submitProof(intent.intentId, settleProof);
  console.log(`Proof submitted. Status: ${submitResult.status}`);

  // Step 5: Poll until completion
  let currentIntent = submitResult;
  const maxAttempts = 60; // 10 minutes max (60 * 10 seconds)
  let attempts = 0;

  while (
    currentIntent.status !== 'TARGET_SETTLED' &&
    currentIntent.status !== 'PARTIAL_SETTLEMENT' &&
    currentIntent.status !== 'EXPIRED' &&
    currentIntent.status !== 'VERIFICATION_FAILED' &&
    attempts < maxAttempts
  ) {
    await new Promise(resolve => setTimeout(resolve, 10000)); // Poll every 10 seconds
    attempts++;

    try {
      currentIntent = await client.getIntent(intent.intentId);
      console.log(`[${attempts}] Status: ${currentIntent.status}`);
    } catch (error) {
      console.error(`Error polling status: ${error}`);
      // Continue polling on transient errors
    }
  }

  // Final status check
  if (currentIntent.status === 'TARGET_SETTLED') {
    console.log('✅ Payment complete!');
    console.log(`Transaction hash: ${currentIntent.targetPayment?.txHash}`);
    return {
      success: true,
      intentId: currentIntent.intentId,
      status: currentIntent.status,
      txHash: currentIntent.targetPayment?.txHash,
    };
  } else {
    console.error(`❌ Payment failed: ${currentIntent.status}`);
    return {
      success: false,
      intentId: currentIntent.intentId,
      status: currentIntent.status,
    };
  }
}

// Usage — payer pays on Base, merchant receives on Base (same-chain).
completeX402PaymentFlow(
  '0x742d35Cc6634C0532925a3b844Bc9e7595f0bEb',
  '10.50',
  'base'
).then(result => {
  console.log('Final result:', result);
});

// 1. Create intent with email + Solana target
const intent = await client.createIntent({
  email: 'merchant@example.com',   // Privy resolves to Solana wallet because target_chain=solana
  amount: '10.50',
  payerChain: 'base',
  targetChain: 'solana',
});

// 2. Sign locally as usual — signing follows payer_chain (Base → EIP-3009).
const settleProof = buildEVMsettleProof(
  intent.paymentRequirements,
  payerAddress,
  privateKey,
);

// 3. Submit and poll until TARGET_SETTLED.
await client.submitProof(intent.intentId, settleProof);

package main

import (
    "context"
    "fmt"
    "log"
    "time"
    "github.com/cross402/usdc-sdk-go"
    "github.com/ethereum/go-ethereum/crypto"
)

func completeX402PaymentFlow(
    ctx context.Context,
    recipient string,
    amount string,
    payerChain string,
) error {
    // Initialize SDK client (public mode, no auth required)
    client, err := pay.NewClient("https://api-pay.agent.tech")
    if err != nil {
        return err
    }

    // Step 1: Generate wallet
    privateKey, err := crypto.GenerateKey()
    if err != nil {
        return err
    }
    payerAddress := crypto.PubkeyToAddress(privateKey.PublicKey).Hex()
    privateKeyHex := fmt.Sprintf("%x", crypto.FromECDSA(privateKey))

    log.Printf("Using payer wallet: %s", payerAddress)

    // Step 2: Create intent
    resp, err := client.CreateIntent(ctx, &pay.CreateIntentRequest{
        Recipient:  recipient,
        Amount:     amount,
        PayerChain: payerChain,
    })
    if err != nil {
        return err
    }

    log.Printf("Intent created: %s", resp.IntentID)
    log.Printf("Status: %s", resp.Status)

    // Step 3: Sign X402 proof locally
    settleProof, err := buildEVMsettleProof(
        resp.PaymentRequirements,
        payerAddress,
        privateKeyHex,
    )
    if err != nil {
        return err
    }

    log.Println("X402 proof signed locally")

    // Step 4: Submit proof
    proofResult, err := client.SubmitProof(ctx, resp.IntentID, settleProof)
    if err != nil {
        return err
    }

    log.Printf("Proof submitted. Status: %s", proofResult.Status)

    // Step 5: Poll until completion
    maxAttempts := 60
    attempts := 0
    currentIntent := proofResult

    for attempts < maxAttempts {
        if currentIntent.Status == pay.StatusTargetSettled ||
           currentIntent.Status == pay.StatusPartialSettlement ||
           currentIntent.Status == pay.StatusExpired ||
           currentIntent.Status == pay.StatusVerificationFailed {
            break
        }

        time.Sleep(10 * time.Second)
        attempts++

        intent, err := client.GetIntent(ctx, resp.IntentID)
        if err != nil {
            log.Printf("Error polling status: %v", err)
            continue
        }

        currentIntent = intent
        log.Printf("[%d] Status: %s", attempts, currentIntent.Status)
    }

    // Final status check
    if currentIntent.Status == pay.StatusTargetSettled {
        log.Println("✅ Payment complete!")
        log.Printf("Transaction hash: %s", currentIntent.TargetPayment.TxHash)
        return nil
    } else {
        return fmt.Errorf("payment failed: %s", currentIntent.Status)
    }
}

stateDiagram-v2
    [*] --> AWAITING_PAYMENT
    AWAITING_PAYMENT --> PENDING: submitProof()
    AWAITING_PAYMENT --> EXPIRED: timeout
    PENDING --> SOURCE_SETTLED: verify + settle
    PENDING --> VERIFICATION_FAILED: invalid
    SOURCE_SETTLED --> TARGET_SETTLING: target transfer
    TARGET_SETTLING --> TARGET_SETTLED: done
    TARGET_SETTLING --> PARTIAL_SETTLEMENT: target not completed

import { PublicPayClient, PayApiError } from '@cross402/usdc';

async function handlePaymentWithRetry(
  client: PublicPayClient,
  intentId: string,
  settleProof: string
) {
  let retries = 0;
  const maxRetries = 3;

  while (retries < maxRetries) {
    try {
      return await client.submitProof(intentId, settleProof);
    } catch (error) {
      if (error instanceof PayApiError) {
        // Don't retry on client errors
        if (error.statusCode === 400 || error.statusCode === 404) {
          throw error;
        }
        // Retry on server errors
        if (error.statusCode === 503 || error.statusCode === 500) {
          retries++;
          if (retries >= maxRetries) {
            throw error;
          }
          await new Promise(resolve => setTimeout(resolve, 1000 * retries));
          continue;
        }
      }
      throw error;
    }
  }
}