Your API needs a Bearer token. Their monitor sends a GET.
Real production endpoints sit behind authentication. They expect Bearer tokens, custom headers, the right HTTP method, and they return status codes outside the 2xx/3xx default. Pingdom and UptimeRobot were built for marketing sites — they choke on anything past GET /. PingForce monitors handle Basic auth, Bearer auth, custom headers, all standard HTTP methods (HEAD/GET/POST/PUT/PATCH/DELETE/OPTIONS), and user-defined "up" status code ranges. You can monitor /api/v1/health behind a token. You can flag 401 as an incident on a protected route. You can POST a real payload and parse the response.