FP4:/ $ df -h
Filesystem      Size Used Avail Use% Mounted on
tmpfs           3.6G 1.8M  3.6G   1% /dev
tmpfs           3.6G    0  3.6G   0% /mnt
/dev/block/dm-2 3.8G 953M  2.8G  25% /
/dev/block/dm-3 399M 339M   51M  87% /system_ext
/dev/block/dm-1 911M 341M  554M  39% /product
/dev/block/dm-4 449M 420M   20M  96% /vendor
/dev/block/dm-0  30M 1.2M   29M   5% /odm
magisk          3.6G 3.8M  3.6G   1% /debug_ramdisk
tmpfs           3.6G 8.0K  3.6G   1% /apex
/dev/block/dm-5 222G  61G  161G  28% /data
magisk          3.6G    0  3.6G   0% /system/app
/dev/fuse       222G  61G  161G  28% /storage/emulated

I was able to run an image without signing trying to sign now getting:

$ nix build --impure
warning: Git tree '/home/orozen/nixpkgs' is dirty
error: builder for '/nix/store/1nqvy0hbxc1s29z5p7l8m7l6kfb7q9j8-instantnoodlep-signed_target_files-2024112323.zip.drv' failed with exit code 1;
       last 1 log lines:
       > Missing KEYSDIR directory, did you use "--option extra-sandbox-paths /keys=..." ?
       For full logs, run 'nix log /nix/store/1nqvy0hbxc1s29z5p7l8m7l6kfb7q9j8-instantnoodlep-signed_target_files-2024112323.zip.drv'.
error: 1 dependencies of derivation '/nix/store/p49s6lqkmwnvs2b7q806byw8indjphnv-instantnoodlep-img-2024112323.zip.drv' failed to build

having this flake:

{
  description = "Robotnix configuration for OnePlus 8 Pro";

  inputs.robotnix.url = "github:nix-community/robotnix/430b818f5e0a94aba9371bebdcc489f636c5e161";

  outputs = { self, robotnix }: {
    robotnixConfigurations."oneplus8pro" = robotnix.lib.robotnixSystem ({ config, pkgs, ... }: {
      # Required options
      device = "instantnoodlep";  # Codename for OnePlus 8 Pro
      flavor = "lineageos";  # Change this to 'lineageos' if you want LineageOS, otherwise keep 'grapheneos' if supported
      androidVersion = 13;

      variant = "user";
      buildDateTime = 1732404420;
      # Optional configurations
      # buildDateTime = 1584398664; # Update if you want to push OTA updates for your custom changes

      # If you have keys for signing, enable this
      signing.enable = true;
      signing.keyStorePath = "/home/orozen/nixpkgs/phone/keys";
      # Enable ccache if you want faster subsequent builds
 
      apps.fdroid.enable = true;
      microg.enable = true;

      # ccache.enable = true;

      webview.chromium.enable = false;
      webview.prebuilt.enable = false;
      apps.chromium.enable = false;
    });

    # Default package for building the image
    defaultPackage.x86_64-linux = self.robotnixConfigurations."oneplus8pro".img;
  };
}

I assume you guys seen this before, I noticed this issue :
https://github.com/nix-community/robotnix/issues/204
but I didn't figure out the solution yet.