If you manage the server you should check your logs, otherwise ask your host to do the same. When configured through cpanel by default, the change is supposed to be made in DNS managed by that server to point a CNAME to Cloudflare. So it sounds like there was an error on your server in that process.
If you’ve changed the default and used full setup then check your nameservers at the registrar instead.
I dont know what UI that is. Is your host a Cloudflare partner? In that case you’d best contact them. If not, your nameservers do not point to Cloudflare but to Nazwa and you would need to fix that.