When adding a custom domain to Vercel, it must go through a process of verification. This process involves changing DNS records.
Once DNS records have been changed, they can take a while to propagate, which means global DNS providers recognise they have been changed. A custom domain added to Vercel will appear as unverified until this process is complete and full propagation has been achieved.
If you have changed the nameservers with your current domain registrar then it usually takes up to 48 hours for these to be reflected globally. This is not something that Vercel have any control over and for certain registrars, this can can slower.
Once nameservers have been changed, you may wish to check the progress of the propagation. There are many third-party tools that do this, such as DNS Checker and DNS Map - these show the state of your DNS records in different regions of the world.
You can also use the terminal to check the nameservers for your domain according by specific DNS providers, some examples are found below:
dig @220.127.116.11 +short NS vercel.com
dig @18.104.22.168 +short NS vercel.com
dig @ns1.vercel-dns.com +short NS vercel.com
Unlike nameserver changes, propagation of CNAME records is usually very quick.
You can also use the terminal to check the CNAME record for your domain according by specific DNS providers, some examples are found below:
dig @22.214.171.124 +short CNAME www.vercel.com
dig @126.96.36.199 +short CNAME www.vercel.com
dig @ns1.vercel-dns.com +short CNAME www.vercel.com