Vercel is currently testing the Anycast methodology for DNS and routing. This methodology allows those using a custom domain to verify it without requiring a change in nameservers.
To verify the domain, add the following records with your DNS provider:
"0 issue letsencrypt.org".
If you followed the instructions above successfully, your domain will be available for use on any Vercel project that you own. All that's required is to add it to the project you wish to use it with.