The facilitator is the piece that turns a signed payment authorization into an on-chain settlement. It lets the resource server accept payments without running its own chain infrastructure.
When you retry a request with a PAYMENT-SIGNATURE, the server hands the signed authorization to a facilitator to verify (is the signature valid, the amount correct, the authorization unused?). After the handler runs successfully, the facilitator submits the transfer on-chain and pays the gas. The server returns the data plus an X-PAYMENT-TX header pointing at the settlement.
As a caller you never interact with the facilitator directly — you just sign and retry. But it is why you do not pay gas (the facilitator does) and why settlement is fast: verification is off-chain and instant, settlement follows in a couple of seconds.
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Browse the full endpoint directory, grab the quickstart, or read the llms.txt manifest. Every endpoint is keyless and pay-per-call.