We look at domains the same way as Google does. For example:
google.com, es.google.com and google.es all are a domain. This means this would result in 3 domains;
However, google.com/es/ is just a path on a domain. So, the domain is the same as google.com/en/
In addition, if your checkout or subscription forms are hosted on subdomains or other (pagebuilder) domains, these are also considered to be separate domains.
A staging-domain will also be considered its own domain, requiring a separate subscription.