Redirects are 300 level HTTP codes, 301 or 302 for example.

Not exactly what is happening here.

Then there's the message below for: Add another domain.

It reads as a separate thing.. and makes more sense, yet most of the time we're adding more subdomains.

In reality we're aliasing or adding another redirect, but not quite domains (not that we can't).

I propose renaming both to something consistent, so if we stick with "Redirects" we also "Add another redirect".