HP scanner nixos 19.03

I am trying to use my scanner that is a wifi one. It is a HP scanner. I have been following: https://nixos.wiki/wiki/Scanners so I have:

sane = {
  enable = true;
  extraBackends = [ pkgs.hplipWithPlugin ];
  extraConfig."hpaio" = ''

I have tried rebooting and running scanimage -L as normal and root users. Still no scanner. Not sure what to do from here.