Monitor ONE x402 endpoint for 30 days and get alerted on changes that break agents: payTo changes (critical — possible takeover/rug), price changes, asset/network changes, 402-spec regressions, delisting, and liveness (down/recovered). Account-free: pay, receive a one-time secret + poll URL. Push to multiple signed HTTPS webhooks and/or Slack/Discord incoming webhooks (up to 5 each per watch). Every push URL is connection-tested before payment — unreachable URLs are rejected with no charge. Edit URLs or cancel early for free via bearer-authed PATCH/DELETE /v1/watch/{id}. Poll the append-only event log; nothing is lost between polls.