If you host multiple subdomains on Vercel throughout separate accounts, you are now able to verify ownership of those subdomains in a self-serve manner via the Vercel Dashboard and API. Adding a subdomain to a project no longer requires the apex domain. Ownership is established via a token that is generated when the subdomain is added to a project and published in the domain owner’s DNS records. This change makes it easier to share domains for Platforms, teams, and collaborators on Vercel.
To learn more check out the UI docs or REST API docs to add a domain to a project and verify that domain if needed.