Bridging x402 to BNB Chain

The x402 protocol, developed by Coinbase, defines how payments can move natively over the internet using HTTP requests. Its reference implementation depends on the EIP-3009 standard (transferWithAuthorization), which most stablecoins on BNB Chain do not support.

This limitation made it impossible to use x402 for gasless payments or API monetization on BNB until now.

The Problem

x402 requires the token contract to support EIP-3009 to validate gasless transfers.
Popular stablecoins on BNB, such as USD1, use the EIP-2612 permit() flow instead.
Developers who wanted to integrate x402 had to modify or fork the official library, adding risk, complexity, and incompatibility across tokens.

Our Solution

We built the first compatibility wrapper that bridges the gap between x402 and non-EIP-3009 tokens. It allows USD1, and soon other stablecoins, to work with x402 without changing the official library.

How It Works

Accepts EIP-3009-style calls (transferWithAuthorization) from the x402 flow.
Converts them internally into EIP-2612 permit() + ERC-20 transferFrom() calls.
Handles gasless execution transparently, allowing wallets with zero BNB balance.
Adds nonce tracking, replay protection, and time window validation for security.

Why This Approach Is Better

No library forks. The official x402 library remains untouched. Full gasless support. Works even if the user has no native tokens. EIP-3009 compatible. Merchants can integrate instantly with no new code. Multi-chain ready. The same pattern applies to Solana, Base, and future ecosystems. Efficient. Around 150k gas per transfer, making it cheaper and safer than direct rewrites.

Architecture

User → Signs EIP-712 Message → Facilitator (pays gas) → Wrapper → USD1 Token

less Copy code

User signs authorization off-chain without gas.
Facilitator submits it on-chain through the wrapper.
Wrapper validates and executes the transfer.
x402 confirms payment settlement.

Integration Example

JavaScript / TypeScript Example

import { ethers } from "ethers";

const WRAPPER = "0x6F212f443Ba6BD5aeeF87e37DEe2480F95b75a36"; // BSC Mainnet
const USD1 = "0x8d0D000Ee44948FC98c9B98A4FA4921476f08B0d";

async function createPayment(signer, to, amount) {
  const domain = {
    name: "X402 BSC Wrapper",
    version: "2",
    chainId: 56,
    verifyingContract: WRAPPER,
  };

  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" },
    ],
  };

  const nonce = ethers.randomBytes(32);
  const value = ethers.parseUnits(amount.toString(), 18);
  const validAfter = Math.floor(Date.now() / 1000) - 60;
  const validBefore = Math.floor(Date.now() / 1000) + 3600;

  const message = {
    from: signer.address,
    to,
    value,
    validAfter,
    validBefore,
    nonce: ethers.hexlify(nonce),
  };

  const signature = await signer.signTypedData(domain, types, message);
  return { ...message, signature };
}
</details> <details> <summary>Solidity Interface</summary>
solidity
Copy code
interface IX402BSCWrapper {
    function transferWithAuthorization(
        address from,
        address to,
        uint256 value,
        uint256 validAfter,
        uint256 validBefore,
        bytes32 nonce,
        bytes calldata signature
    ) external;
}
</details>

Extending the Model

This wrapper design will next support USDF, part of the ÁSTER ecosystem, enabling AI agents and vibe-coding bots to use x402 gaslessly during competitions and beyond.

The goal is to make x402 fully chain-agnostic, unlocking instant, fee-less payments for any token starting with BNB.

Security Highlights

Replay protection with unique nonces
Timestamp validation using validAfter and validBefore
EIP-712 domain binding per chain
No admin privileges or upgrade paths
Immutable and verified on BscScan

Conclusion

The x444 wrapper is the missing piece that finally makes x402 usable on BNB Chain. No engineering hacks or heavy integrations. Only a clean, efficient compatibility layer that keeps the protocol’s integrity while expanding its reach.

This is how gasless payments move from theory to reality.

Last updated 1 day ago