“URL not in property” when I submit a removal request for an old subdomain’s URLs to Google Search Console

Solution for “URL not in property” when I submit a removal request for an old subdomain’s URLs to Google Search Console
is Given Below:

I have website called example.com. Somehow an admin URL admin.example.com was crawled (more than 2-3 years ago) and it has more than 150 search results.

Now the technology stack used to create that site is outdated. We remade the website with a completely new Technology stack.
Now I have example.com/sitemap.xml which doesn’t have admin.example.com related URLs.

I want to submit a removal request for admin.example.com in my Google Search Console property for example.com. However it says “URL not in property”

So how do I submit the removal request for the subdomain? Are there alternatives to achieve this? We will block or redirect admin.example.com, but how do we remove it from the Google search index?

The Search Console doc mention two types of properties, URL-prefix and domain. This seems to be because Google doesn’t recognize your subdomain, which according to your comment can be fixed by adding the subdomain as another property.