I created a nixos machine on VirtualBox and can “nix ping-store” to it (I assume that no result is success, after getting error messages when I made a mistake). However, when I try to use it build something, I always get the error “cannot add path … because it lacks a valid signature”. Is there something I need to do to make sure that signatures are valid? I was reading about GPG signatures but couldn’t see that there was anything I was supposed to do.