If you go to the website IP6Only.me or IP4Only.me the following notice is posted:
!! NOTICE !!
Notice: The owner of ip4.me/ip6.me, Kevin Loch, passed away.
The Kevin M Loch Estate will be shutting down Kevin's websites in the near future (4/1/2025).
Inquiries for purchasing Kevin's domains may be sent to ipadmin@dulles-ix.net.
Click this link to continue to your ip4/ip6 address reporting Website
List of Websites impacted: ip4.me, ip4only.me
ip6addr.com, ip6addr.net, ip6addr.org
ip6.me, ip6only.me
ipv6addr.com, ipv6addr.net, ipv6addr.org
onlyip4.me, onlyip6.me
whatismyipv6address.com, whatismyipv6address.net, whatismyipv6address.org
whatismyv6.com, whatismyv6.net, whatismyv6.org
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I've created a Github Issue in opnsense/plugins but for anyone using this 'Check IP Method' for Dynamic DNS ddclient, should consider an alternative.