nix build .#nixosConfigurations.sandbox.config.system.build.toplevel
nix build .#nixosConfigurations.sandbox.config.system.build.vm
nix build .#nixosConfigurations.sandbox.config.system.build.vm
./result/bin/run-nixos-vm
Note that image state is stored in a qcow2 image, you may wish to remove this if state from previous builds is interfering with your current build:
rm nixos.qcow2; ./result/bin/run-nixos-vm
Before running any scripts, it's important to wait for the BFT nodes to finish starting up (check for the existence of /var/lib/cardano-node/state/node-bft1/node.sock.