SpendPreflightHow x402 payment works
A quote is data. Signing is authority. Keep the decision between them.
Live features and staging previews are distinguished. Index coverage is not yet available.
The sequence
1. Request a resource without payment. 2. Read the402 challenge. 3. Select and validate the exact scheme, network, asset, amount and payTo. 4. Run local rules and optional SpendPreflight screening. 5. Sign only on an approved allow. 6. Retry with the payment authorization. The seller verifies and settles through its facilitator, then returns the result and payment response.
USDC on Base
Our live service receives USDC on eip155:8453, asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913, payTo 0xBf4164e07552e4c1b1B1597E72C7acAA3F0a1c58. Six decimal places means 10000 atomic units=$0.01, 20000=$0.02. The cached endpoint lookup is 5000=$0.005. A familiar token address on another chain is not equivalent.
Two different payments
The screening call pays SpendPreflight for a decision. Any later merchant payment is separate, chosen and signed by your client. We never sign, settle or custody the merchant payment under review. A paid hold/block is a delivered screening result, not a rejected screening request.
Uncertain settlement
A lost settlement response may follow an actual transfer. Inspect the original nonce/transaction before retrying. Changing facilitator or signing a new authorization can double-pay. Our failure handling returns an explicit unknown outcome; it does not promise a refund or automatic fallback.