Put firewall behind cloudflare

hi everyone
i have a kerio firewall which i want to protect from DDOS attacks
ive added my domain to Cloudflare and its working
and ive created A record pointing to my firewall IP but its not working
any solution?
is it even possible to put firewall behind Cloudflare?

Sure. Either you need port forwardings, or MIPs, or…
Also ensure that Cloudflare is whitelisted

The following ports are proxied by Cloudflare: