i bought a new domain few days ago at cloudflare but that status still "Invalid nameserver"

[midnight tundra]

Do you see the domain under Domain Registration -> Manage Domains?

or did you register it through Domain Registration -> Register Domains? or what do you mean you bought it?

[final crater]

I created a free account in cloudflare and then serach for the domain i want to buy and bought it

just like add a domain if you already have a domain

[midnight tundra]

So, you paid for the registration (should be like ~10 usd or w/e) and see it under Domain Registration -> Manage Domains?

[final crater]

yes

[midnight tundra]

What's the status under Domain Registration -> Manage Domains?

[final crater]

status is orange which i assumed the same as invalid nameserver on the Overview page

[midnight tundra]

Under status it has an orange/red dot instead of "Active"?

If so, looks like there was an issue with the registration process.
It's possible you got an email asking for verification info from Cloudflare, would check spam and such.
Otherwise I'd registrar ticket asking about it.
The invalid nameservers is just a symptom that the domain registration didn't go through/the domain is still not registered

[final crater]

i tried to register it again an it worked thanks