Issue of /bin/ping not found even when present in Dockerfile

My web app is using /bin/ping in backend and iputils-ping is present in base docker image. Any idea why I get /bin/ping not found now when app is running in fly.io?

Thanks.

Missed to attach Dockerfile - uptime-kuma/dockerfile at master · louislam/uptime-kuma · GitHub

This is what needed iputils-ping in background to run icmp checks.