A2A capability discovery does not grant payment authority.
The older A2A page advertised x402/1.0 and XRPL-oriented payment headers. Those instructions are retired from current ScriptMasterLabs authority.
Discover the selected capability, call its exact target resource, read the fresh PAYMENT-REQUIRED challenge, and let the caller decide whether to create the matching PAYMENT-SIGNATURE.
Current SML paid-resource defaults are Base mainnet eip155:8453 and USDC. A 402 challenge or signature is not settlement proof.
Current agent card → · Current x402 discovery →
How an agent should pay another agent?
- Discover. Read the other agent's capability card or MCP tool list to find the job you need. Discovery is free and grants no right to spend.
- Request the resource. Call the exact paid endpoint. If payment is needed it answers with HTTP 402 and a
PAYMENT-REQUIREDchallenge listing the price, asset, network and receiver. - Check policy. The paying agent compares those exact terms with its own budget, allow-list and per-call cap. If anything does not match, it stops.
- Authorize. Only then does its wallet create a
PAYMENT-SIGNATUREfor that one challenge and retry the request. - Verify. A
PAYMENT-RESPONSEwith a settlement reference shows the payment settled. The caller still checks that the delivered result is what it asked for.
Why discovery and payment stay separate?
A capability card can be cached, copied or out of date. The live challenge cannot, because the server issues it for that request. Keeping payment authority in the fresh challenge and in the caller's own policy means no directory, prompt or old page can make an agent pay the wrong receiver or the wrong amount.
See the x402 Gateway to inspect live terms before any agent pays.