Subdomains are supported through the Wildcard Subdomain feature, available on all paid plans (Launch, Scale, and Optimize).
How it works
A wildcard subdomain is defined as *.yourdomain.com, which covers any single-level subdomain under your root domain - for example, app.yourdomain.com or portal.yourdomain.com.
Single-level subdomains only
It is important to note that wildcard matching only applies to a single subdomain level. Multi-level subdomains such as portal.dev.domain.com or portal.prod.domain.com are not covered by a *.domain.com wildcard. Each domain entry must match the exact structure being used.
How to add a subdomain
To add a wildcard subdomain to your project, navigate to your project's Allowed Domains settings and add your domain in the *.yourdomain.com format.