DNS is the first step
An AAAA record advertises IPv6 reachability but does not prove the service or firewall actually works over IPv6.
Website + network
Test the website over IPv6, not just its DNS record.
Find public AAAA addresses and force the HTTP/HTTPS request path to use IPv6 through the same restricted diagnostic client.
Result
Diagnostic result
Force IPv6
This check does not quietly fall back to IPv4. Each redirect hop must also be reachable through a public IPv6 address.
Validate HTTPS normally
For HTTPS targets the normal hostname and certificate validation still applies over IPv6.
Keep v4/v6 behavior aligned
A site can appear healthy over IPv4 while IPv6 users see a timeout, stale vhost or different certificate.