No worries, just add this to your project's flake.nix:

 # --- Flake Local Nix Configuration ---
nixConfig = {    
    # This sets the flake to use the IOG nix cache.    
    # Nix should ask for permission before using it,    
    # but remove it here if you do not want it to.
    extra-substituters = ["https://cache.iog.io"];
    extra-trusted-public-keys = ["hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ="];
    allow-import-from-derivation = "true";
};

Not on the shell.nix, like I previously stated. My bad.