Custom subdomain not resolving on branch deploy

Just as a wee update, I’ve also seen [Support Guide] How to use Netlify’s branch deploy feature without Netlify DNS

about custom subdomains for branch deploys and I’ve configured that too.

So currently I’ve got:
valuable CNAME valuable-landing-page.netlify.app 3600
and
dev.valuable CNAME dev--valuable-landing-page.netlify.app 3600

Configured correctly.

I’ve got a note in my HTTPS panel:
valuable.ringfence.nz doesn't appear to be served by Netlify

That has appeared with these changes. Should I expect that to disappear?

Also I read in the above link that I could ask for SSL certs to be extended to include my dev branch deploy as well. I’d really appreciate it if someone could help me out with that.

I hope that’s everything I need! I’ve already got this exact setup working on another Netlify site but I configured that a couple of years ago. It’s been a journey of rediscovery!

Thanks so much for all your help Luke! I appreciate it!