x402 v2
x402 extends HTTP 402 Payment Required with machine-readable payment requirements. A protected service advertises the network, asset, amount, recipient, scheme, and authorization window; the client then retries with a signed payment payload.
MPP
MPP standardizes machine-to-machine payments through the HTTP authentication model. The server sends a WWW-Authenticate: Payment challenge, and a successful response can include a Payment-Receipt for downstream reconciliation.
EIP-712
EIP-712 defines typed structured-data hashing and signing. Wallets can present the payment fields to the signer in a deterministic domain, reducing ambiguity compared with opaque message signing.
ERC-3009
ERC-3009 TransferWithAuthorization enables a token holder to authorize a transfer using an offchain signature. The authorization binds the source, destination, value, validity window, and nonce; the Facilitator submits it onchain and pays the network fee.
Network and settlement asset
This PoC uses Base Sepolia and Circle USDC. The network is identified as eip155:84532, and the configured USDC contract uses six decimal places.