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 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) 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
• MPP — alternative rail
• /subscribe reference — full schema

llms.txt OpenAPI MCP server card x402.json mpp.json Agent card Agent skills SKILL.md sitemap.xml Glossary