# Welcome to NERO 402

> An AA-native settlement scheme for x402, with a reference implementation on NERO Chain.

NERO 402 is the first production implementation of an AA-native settlement scheme for the [x402 V2](https://www.x402.org/writing/x402-v2-launch) HTTP payment protocol. Where the upstream `exact` scheme requires the paying account to be an EOA capable of signing EIP-3009 typed data, the `aa-native` scheme defined here lets ERC-4337 smart contract wallets pay merchants directly. A paymaster sponsors the gas, so the agent never needs to hold the chain's native asset.

This site is the developer reference for everything in the stack:

- The four `@nerochain/x402-*` packages.
- The deployed `SettlementContract` on NERO mainnet and testnet.
- The reference facilitator service that speaks both `exact` and `aa-native`.
- The whitepaper that specifies the scheme.

## Pick your path

If you are an **agent author** wanting to call paid APIs, start with [Quickstart for agents](/docs/getting-started/agents).

If you are a **merchant** wanting to gate an endpoint behind payment, start with [Quickstart for merchants](/docs/getting-started/merchants).

If you want the **protocol details**, read the [whitepaper](/whitepaper.pdf) or the [aa-native scheme](/docs/core-concepts/aa-native-scheme) page.

## What's distinctive about NERO 402

- **Smart contract wallet payments.** The paying account is an ERC-4337 SCW. EOAs are still supported via the `exact` scheme.
- **Gas-sponsored from day one.** Type-0 paymaster sponsorship means the agent's SCW spends zero NERO native on every paid call, including its own first-time deployment.
- **Stable wire format.** The envelope is the canonical x402 V2 payload (`@x402/core@2.11.0`); only the inner `payload` differs per scheme. Unmodified upstream `exact` clients interoperate with the reference facilitator out of the box.
- **One on-chain settlement contract.** Replay-protected, owner-allowlisted tokens, UUPS-upgradeable. Merchants are arguments to `settle()`, not separate deployments.

## What's not done yet

The settlement contract has not been audited; v1.0 publication of the SDK packages waits on that. Mainnet deployments to date have processed sub-dollar quantities of USDT under controlled conditions. The whitepaper is published as a draft for community review prior to upstream submission.