Most of the major TV providers are participating providers across all our platforms. i.e. Comcast, AT&T, DirecTV, etc. In some cases, certain TV providers may only be available on certain platforms.
If your provider does not support FOX but does support FX and/or National Geographic, you will not be able to sign into FOX NOW. Instead, you should use FXNOW or Nat Geo TV to watch programming from those networks.