Background image not showing

[hidraulicChicken]

Hey folks, I'm on NixOS 23.11 with sway and tried everything to get the background showing, but never ever shows up. Here are my configs: /etc/greetd/regreet.toml

[GTK]
application_prefer_dark_theme = true
cursor_theme_name = "Adwaita"
font_name = "JetBrainsMonoNerdFontMono-Regular"
icon_theme_name = "Adwaita"
theme_name = "Adwaita"

[background]
path = "/tmp/fallout_loading.jpg"

[commands]
poweroff = ["systemctl", "poweroff"]
reboot = ["systemctl", "reboot"] 

swayConfig = pkgs.writeText "greetd-sway-config" ''
    # `-l` activates layer-shell mode. Notice that `swaymsg exit` will run after gtkgreet.
    exec "${pkgs.greetd.regreet}/bin/regreet -l debug  &> /tmp/regreet.log; swaymsg exit"
    bindsym Mod4+shift+e exec swaynag \
	-t warning \
	-m 'What do you want to do?' \
	-b 'Poweroff' 'systemctl poweroff' \
	-b 'Reboot' 'systemctl reboot'
    include /home/gergoe/.config/sway/config
  '';

greetd command: dbus-run-session ${pkgs.sway}/bin/sway --config ${swayConfig}

regreet.log

background: -rwxrwxrwx 1 myuser users 275K 2024-04-30 14:02 /tmp/fallout_loading.jpg

Sadly the I couldn't decipher the error message: Gtk-WARNING **: 14:27:41.009: Theme parser warning: :6:17-18: Empty declaration

Please let me know what else I could check/set.