Recently, I was unable to change the location on my Mullvad VPN from other thing other than sweden. Even using the mullvad cli tool I would keep getting errors like:

invalid argument for type conversion: missing custom lists settings

it turned out to somehow a mismatch in versions where everything was running 2023.6 but my mullvad cli was using 2023.5. So I ended up fixing this by changing my config to:

  services.mullvad-vpn = {
    enable = true;
    package = pkgs.mullvad-vpn;

Where setting the package to mullvad-vpn, which then installed the correct version of the mullvad cli tool and I was then able to change locations using the gui as per usual. No idea why there was a version mismatch.