AUTX built and operated a full x402 payment gateway on Base mainnet through the Coinbase CDP facilitator: 402 envelopes, verify and settle, replay protection, metering, and a real-money canary that proved the pipeline every day. We also probed the liveness of every service in the public x402 catalog. One in five listed endpoints is dead, and some lose money on every malformed request.
The marketplace is archived. The engineering is available.
What we do
x402 Paywall Audit.
Real USDC settles against your endpoints, a six-point failure checklist, and a findings memo with on-chain proof of every test. Fixed price, three business days.
x402 Integration.
Your API accepting USDC on Base, verified end to end with real settles before handoff: envelopes, facilitator verify and settle, replay protection, v1 and v2 shapes.
Paywall monitoring.
Scheduled real-money canary settles against your paywall with alerts and on-chain proof. You find out it broke before your buyers do.
The failure checklist
Settle-before-validate ordering. We found a live merchant charging buyers before validating requests. Every malformed call costs them money.
v1 vs v2 envelope shapes. 4 of 18 merchants we probed still serve maxAmountRequired. Buyers on the other shape silently fail.
Replay protection. Nonce plus payer must be enforced. We test it with a real duplicate.
GET with body. Some load balancers reject it before your app ever sees the request.
Bot blocks. Default client user agents trip WAF rules and turn paying agents away.
Dead listings. 21.5% of cataloged x402 endpoints are dead. Yours might be listed somewhere you forgot.