The nameservers are showing in the whois data, but aren’t served by the parent zone:
dig +trace +nodnssec volunteer.cv
; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> +trace +nodnssec volunteer.cv
;; global options: +cmd
...
cv. 172800 IN NS c.dns.pt.
cv. 172800 IN NS ns.dns.cv.
cv. 172800 IN NS anyc.dnsnode.net.
cv. 172800 IN NS cv01.dns.pt.
;; Received 281 bytes from 192.58.128.30#53(j.root-servers.net) in 1 ms
cv. 300 IN SOA ns.dns.cv. dnsop.dns.cv. 2024090202 86400 7200 2592000 300
;; Received 120 bytes from 2001:500:14:6105:ad::1#53(c.dns.pt) in 7 ms
So right now, the domain is not active, despite the status code saying that it is. This is something you need to discuss with your registrar.