Does that have to be a publicly accessible URL, or can it also be on a URL based on a share Infuse already has access to like a cloud service, or Plex?
It can be any http link as long as it is accessible from your current location.
SMB, NFS, UPnP, etc… cannot be used here.
You can also add links that are not accessible in your current location, but the download feature would not be able to be used until you are in a location where the link was working.