In an x402 flow, the resource server can outsource the two hard steps to a facilitator: POST /verify confirms a signed payment payload meets the declared payment requirements (without touching the chain), and POST /settle submits the validated payment on-chain and watches for confirmation. A GET /supported endpoint advertises which schemes and networks the facilitator handles.
Facilitators are optional but recommended — they're why an API seller can accept stablecoins with a few lines of middleware. Well-known facilitators include Coinbase's CDP facilitator (fee-free settlement on Base and Solana) and PayAI (Solana-first, multi-network). In the v2 spec, facilitators and payment schemes are pluggable, so new networks can be added without changing the protocol.
No — a server can verify and settle payments itself. But a facilitator removes the need to run blockchain infrastructure, which is why most x402 sellers use one (e.g. Coinbase CDP or PayAI).
Verify checks the signed payment payload against the server's payment requirements off-chain; settle actually broadcasts the transaction to the blockchain and monitors it until confirmed.