402 Payment Required with a price, and the client retries with a
signed payment. On Metal, that payment authorizes a transfer of *USDZ,
Metal’s dollar token. The agent only signs the payment; the seller
passes it to the facilitator, which submits it on
chain and pays the gas.
Metal’s facilitator settles two schemes: exact, one transfer per
payment, and bajillion, Metal’s clearing, a running total against one
deposit.
The exact flow
exact is standard x402: the agent signs one transfer of *USDZ for one
price, and the facilitator submits it as one transaction. It is the same
authorized payment any seller on
Metal accepts, which is why an agent can pay from an account it does not
own, within limits the owner set.
The bajillion flow
Clearing is for frequent, low-cost purchases, where a transaction per
payment would cost more than the purchase. The agent deposits *USDZ once
and signs a running total with each request; the clearing
service answers each with a signed receipt and certifies the totals on
chain every few seconds.
In both, the seller pays nothing and the agent pays no gas for a payment.
Under clearing each side pays the gas of its own deposits and withdrawals.
Pay for an API
The agent’s side: an account, funds and a paid request.
Facilitator
Endpoints, limits, refusal reasons and retries.