Learn · updated 1 Nov 2026
How to set up x402 payments as a merchant
Answer a 402 with exact payment requirements, then verify and settle the buyer's signed authorisation before serving. Nevarn's facilitator speaks x402 version 2 only: it checks that the payment goes to one of your receiving accounts for the exact amount, then settles it once through its relayer; in UCP checkout, Decionis rules on the exact intent first.
What the buyer receives
On a 402 your server returns a PAYMENT-REQUIRED header: the scheme, the network, an EIP-3009 asset such as USDC, the exact amount and the recipient, which must be one of your receiving accounts. The buyer signs an authorisation for exactly that amount and retries with a PAYMENT-SIGNATURE header.
Only version 2 is spoken. The version 1 headers and fields are refused by name rather than half-supported.
Verify, then settle once
Your server passes the payload and the requirements to Nevarn's facilitator, at /machine/verify and then /machine/settle, using a merchant API key scoped to facilitator use. Verification checks the advertised requirements, the recipient, the amount, the validity window, the signature (an ordinary account or a contract account), that the nonce is unused on chain, and the payer's balance. A bad payment comes back with its reason.
Settlement submits the signed transfer from Nevarn's relayer, which pays the gas and cannot change the recipient or the amount the buyer signed.
What it costs
Merchants pay 0.5% of each settled payment, with no monthly fee. The payment reaches your wallet in full; the fee is recorded in your books as owed to Nevarn.
Where the rollout stands
The complete UCP discovery and checkout path is built and tested, but remains feature-gated and disabled by default. As of 1 Nov 2026, Nevarn does not run a live UCP merchant network, has no external merchant adoption to report, and supports payment only on configured USDC paths.
Questions people ask
Does Nevarn support x402 version 1?
No. Nevarn speaks x402 version 2 only. The version 1 headers, the JSON body on the 402, maxAmountRequired, and network names such as base are refused with invalid_x402_version rather than half-supported.
Who pays the gas when an x402 payment settles?
Nevarn's relayer. Settlement calls transferWithAuthorization on the token from the platform's relayer, which pays the gas and cannot change the recipient or the amount the buyer signed.
What is the difference between UCP and x402?
UCP describes how an agent discovers a merchant, searches products, and manages a checkout session. The x402 payment handler supplies the exact stablecoin payment requirements and signed credential used to complete that checkout. Nevarn connects the two and puts Decionis immediately before consequential settlement.