How to get a free Google-provided domain (for example, yourapp.page.link)

I am following an example to add an email link, but after I click on Dynamic Links, it doesn't provide me with a default url, like in the picture (flutterauth.page.link). I get an empty box, no dropdown.

How do I get a Google provided page.link subdomain, like in the picture?

This is what mine looks like:

I figured out. It's very simple. The url is not pre-created, it doesn't show up by default. You have to start typing, and then you can create a url, if the url link is not taken.

Afer this, you will get a message:

myapp.page.link has been verified and approved for use