CSF Ping problem from external services

I have problem for about several days about ping on my server.

I'm using the alertra for check uptime on my websites also server, everything looks as online and websites are working without any problem but my ping rule on alertra returns and notify my as server is offline. After about one hour, it alerts me as server is okay and no problem.

But server is working, also websites runs perfectly. And i can ping the server from my local computer. Also, i've added the alertra global server ip's to csf allow firewall list.

P.S: I didn't see any problem before with same configurations on server and alertra.

So what is the problem you thoughts ?

Thanks

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My ping rule on the alertra is directly to server main ip. Interesting is that all of alertra servers return as ping fail.

Websites are checking over cloudflare of course (i check the text on the footer for webpage health)

Btw; do you have any advice for check the websites uptime which have call and sms support?