How to run multiple Reflex apps in parallel using subpaths?

[luator]

I'm trying to figure out how I can run multiple Reflex apps on the same server using sub-paths (e.g. example.com/app1, example.comm/app2).
I found that rx.Config has a parameter frontend_path which I guess is needed for this. However, I cannot figure out, how to make it work. For a quick test, I use an existing app that works as is. When I add frontend_path="/foo" to the config and start it locally with reflex run, it prints

App running at: http://localhost:3000/foo

as I would expect. However, when actually opening that URL, I just get an unformatted "Not Found". So obviously, I'm missing something.

Unfortunately, the documentation doesn't help either. I vaguely remember that in the past there was a list of available config parameters somewhere, probably on https://reflex.dev/docs/api-reference/config/, but it seems to be gone...