URL Path Variable (as first path segment)

I’m looking to create a one-page site where the first path segment is a variable. In the editor, it looks like it’s going to work (below), however I get a 404 when trying to reach the page with a path included.

Screenshot 2024-07-12 at 9.18.03 PM

Screenshot 2024-07-12 at 9.18.38 PM

It DOES work as expected if I put the variable as the second path segment like below.

Screenshot 2024-07-12 at 9.19.30 PM

Is it not actually possible to use a variable as the first path segment? Thanks!