Payments and nonces

The 402 challenge

An unpaid request to a paid route returns HTTP 402 with the payment challenge for that URL: a WWW-Authenticate header on /v1/* (MPP) and a PAYMENT-REQUIRED header on /x402/* (x402). One rail per URL; the other rail on the same URL returns 400 and is not charged.

Settle after serve

Payment is settled only after the completion is produced. Requests that fail before a result is produced are not charged.

The client nonce

• Paid requests carry X-Omni-Client-Nonce: <22-128 base64url characters>. It is required.
• The client generates it randomly before paying, keeps it, and uses a fresh one for every payment.
• A missing or malformed nonce returns 400 (client_nonce_required or bad_client_nonce) and the request is not charged.
• The same credential with the same nonce returns the stored result of that payment without a second charge.

N=$(openssl rand -base64 24 | tr '+/' '-_' | tr -d '=')

Rails