Trouble installing package from 20.09 channel

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I am trying to install the version of RunwayML listed there 0.14.3

I am using Ubuntu and entered nix-env -iA nixpkgs. runwayml in the terminal, but got

runwayml is now a webapp

Is there not a way to download the appimage directly somehow?

runwayml from nixos-20.09 should be fine. But it seems to be removed from the newer channels and simply defined as

runwayml = throw "runwayml is now a webapp"; # added 2021-04-17

You might be using a newer channel instead of nixos-20.09. You can use nix-info to confirm this.

You could just use the following for a simple installation:

$ nix-env -f https://github.com/NixOS/nixpkgs/archive/refs/tags/20.09.zip -iA runwayml

If you would like to install more stuff from the 20.09 release, it’s better to add it to the channels and then use someting:

$ nix-env -iA the_name_you_gave_to_the_20_09_channel.runwayml

happy hacking