The domains are added to the whole website, not to the specific applications. Each domain added to the website is an alias to the website domain. The application added in the website domain work automatically in every domain that is being added to the website.
Let’s suppose that I have a website megi.megiteam.com – I can add the applications at the following address:
If I add the catsblog.com domain to the website, all the previously added addresses will start to work together with it.