Give sekani.app an IPv6 address Ask your hosting provider for the site's IPv6 address (or the hostname to point at), then publish it as an AAAA record. If your host doesn't offer IPv6, a proxy that does can sit in front. How to add an AAAA record
www.sekani.app is hosted on Railway, which has no IPv6 It points at uvofh1tr.up.railway.app, and that name has no AAAA record — so nothing you add in your own DNS can give it IPv6. Put an IPv6-capable proxy in front (Cloudflare's proxied DNS does this), or host somewhere that offers IPv6. Which platforms offer IPv6
Mail servers without IPv6 Your domain's mail goes to its own address, which has no AAAA record.
Nameservers without IPv6 nsb1.squarespacedns.com, nsb2.squarespacedns.com, nsb3.squarespacedns.com, nsb4.squarespacedns.com all have no AAAA record, so a resolver that only speaks IPv6 can't look your domain up. Most DNS providers offer IPv6 nameservers; ask yours, or move DNS to one that does.
Visitors on IPv6-only networks (many mobile carriers) can still reach it, but only through a translator their carrier runs (NAT64). The site itself has no IPv6 address — and you can't make one up from the IPv4. Why some hosts don't offer it
Copy the evidence— a citation-ready record of this measurement