Machine Payments Protocol

The Machine Payments Protocol (MPP) is an open specification for charging HTTP endpoints in stablecoins on Solana. It plugs into the x402 standard: a server returns a 402 Payment Required response describing the price, the recipient address, and a payment reference; the client pays in USDC on Solana, retries with the transaction signature, and the server verifies on-chain before responding.

Design goals

• Sub-second settlement. USDC on Solana confirms in well under a second, so paying per API call is not a bottleneck.
• Sub-cent fees. Network fees stay negligible even on micro-payments.
• No accounts or API keys. The on-chain payment is the authorization — agents and servers don’t exchange credentials.
• Replay-safe. Each transaction signature is consumed atomically by the server (e.g. Redis SETNX) so a single payment can’t unlock the endpoint twice.
• Open spec. Any server or client can implement MPP without permission or licensing.

How it relates to Solobank

Solobank implements both sides of MPP. The SDK ships a client that handles the 402 → pay → retry loop automatically and a server middleware that verifies on-chain payments and atomically consumes the signature. Solobank’s agent wallet signs the payment, the MCP server exposes it as a tool, and any HTTP endpoint can accept payments with about five lines of code.