Hi, I am trying to add domain, which I bought “agctrencin.sk”. But Cloudflare still showing that domain is not registered. I bough it few days ago. I already changed NS records to Cloudflare.
You need to have working nameservers BEFORE you try and add your domain to Cloudflare. You need to change the nameservers at your Registrar to a working set of nameservers for your domain, then start to add the domain to Cloudflare.
The nameservers that Cloudflare assign you for your domain may not be the same as the two nameservers you have for all your other Cloudflare domains, so you cannot change the nameservers first, and then add the site to your Cloudflare account.