There’s not enough information here. What exactly is the problem? Do you have any logs to show the issue?
Generally, I recommend using subdomains because it’s cleaner. If you need local access, you can do something like radarr.domain.com, :8081 { to listen on another port for local access.
But if you must use a subpath instead, then you need to configure a UrlBase in Radarr I think:
Sounds like a chronic case of the subfolder problem.
You can’t put your app in a subfolder without setting the base URL. The base URL must match the subfolder. This is required for asset links to line up. Explained further in this wiki post: