You cant have pointed them to Cloudflare as the domain is - obviously - not on Cloudflare yet and hence Cloudflare cant have provided you with nameservers for that domain.
You need to make sure the domain points to valid nameservers before adding it to Cloudflare.
A search - as you were prompted to do - would have actually revealed that quickly.
Please calm down. I am not here to argue with you, if you cant help please stop spamming.
Again, I have already changed them to valid nameservers and tried. It does not help.
Excuse me? I should calm down? I am telling you what to do to fix your issue and you tell me to calm down? And I am spamming? Seriously, you have a nerve.
And no, your domain does not point to valid nameservers as you claim, but still to Cloudflare.
Asked my client to change nameserver back to domain registerar default already, if you understand pain for asking clients to change nameservers.
It’s like rocket science for non technical people.