---
title: x402 (USDC on Base) — Payment
description: Coinbase-verified payments over USDC on Base. Sign once, settle once, get your token.
url: https://agentnumber.really.com/docs/payment/x402
doc_version: "1.0.0"
last_updated: "2026-05-15"
---

> ## Documentation index
> Fetch the complete documentation index at: https://agentnumber.really.com/llms.txt
> Use this file to discover all available pages before exploring further.

# x402 (USDC on Base)

> Coinbase-verified payments over USDC on Base. Sign once, settle once, get your token. No gas required from the paying wallet.

## How the rail works

1. [`POST /subscribe`](/docs/reference/subscribe) with no payment header → server returns `402` with the challenge body.
2. Read `accepts[].network`, `amount`, `asset`, `payTo`.
3. Sign an EIP-3009 `transferWithAuthorization` for that amount + asset + payTo, with your wallet's private key.
4. Base64-encode the signed payload.
5. Re-POST `/subscribe` with `X-PAYMENT: <base64>`.
6. The Coinbase x402 facilitator ([x402.org](https://www.x402.org/)) verifies the signature, settles on-chain.
7. Server issues your bearer + binds the number to your wallet.

## Network

Production settles in USDC on Base mainnet. Always read the asset address and amount from the live 402 challenge body at runtime — don't copy any address out of these docs.

## Why x402

- **No gas from the paying wallet.** Settlement happens via meta-transaction; the facilitator pays gas.
- **Coinbase-verified.** Mature settlement infrastructure, predictable confirmation latency.
- **HTTP-native.** The 402 challenge + retry pattern is just HTTP.

## See also

- [Payment overview](/docs/payment)
- [MPP](/docs/payment/mpp) — alternative rail
- [/subscribe reference](/docs/reference/subscribe) — full schema

## Sitemap

- [Overview](/docs/)
- [Quickstart](/docs/quickstart)
- [Authentication](/docs/auth)
- [SMS](/docs/sms)
- [Voice](/docs/voice)
- [MCP](/docs/mcp)
- [Payment](/docs/payment)

See the full [sitemap.md](/sitemap.md) for the complete index of docs pages.

---

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