I won’t argue about whether Cloudflare’s chosen validation method is the most appropriate or not, the point is that - for some or several reasons - the company has chosen to validate domains in that way and it is well documented on this support page (referenced from the link that @sdayman had already shared):
Before a domain can be added to Cloudflare, the domain must return NS records for valid, working nameservers. NS records can be checked via third-party online tools such as https://www.whatsmydns.net/#NS/ or via a command-line terminal using a dig command:
dig +short ns cloudflare.com
ns3.cloudflare.com. ns4.cloudflare.com. ns5.cloudflare.com. ns6.cloudflare.com. ns7.cloudflare.com.
Additionally, the domain must return a valid SOA record when queried. SOA records can be checked via third-party online tools such as https://www.whatsmydns.net/#SOA/ or via a command-line terminal:
dig +short soa cloudflare.com
ns3.cloudflare.com. dns.cloudflare.com. 2029202248 10000 2400 604800 300
Note that both queries
dig +short ns develrox.cl and
dig +short soa develrox.cl do not return any value - and that’s why the domain cannot be validated.
As @MarkMeyer said, providing nameservers to newly registered domains is the job of the registrars - and it’s really unusual to find cases where this doesn’t happen.
I suggest that you first contact your registrar to clarify if they could provide you with temporary name servers just in order to validate the domain and then change them to those provided by Cloudflare.
If they can’t help, please contact Cloudflare support and ask if there is an alternative to the current method.
I hope this issue will be solved soon and that it won’t take long for you to make use of Cloudflare’s amazing features!