Today a client bought a domain in my hosting and I point the dns to his own vps in which he has installed plesk, but when I put cloudflare to the domain it stopped working. What could be happening, can anyone help me with this problem?
You need to follow Cloudflare setup properly and have the NAMESERVERS reflect Cloudflare servers. Then in there, you need to load the DNS records to point to the Plesk.
I dont use Cloudflare as it tends to cause issues. and i have a Plesk server working beautifully.