I cannot get sops-nix to import my secrets properly

Question

I'm using sops-nix in my configuration, and I want to import some secrets to use with Syncthing, but I cannot get it to work.

  sops = {
    defaultSopsFile = ../../secrets/secrets.yaml;
    defaultSopsFormat = "yaml";
    age = {
      sshKeyPaths = [ "/home/horseman/.ssh/id_ed25519" ];
      keyFile = "/home/horseman/.config/sops/age/keys.txt";
      generateKey = true;
    };

    secrets = {
      "syncthing/luna".owner = "horseman";
      "syncthing/terra".owner = "horseman";
      "syncthing/solis".owner = "horseman";
      "syncthing/gui_user".owner = "horseman";
      "syncthing/gui_password".owner = "horseman";

    };
  };

  services.syncthing = {
    enable = true;
    user = "horseman";
    dataDir = "/home/horseman";
    configDir = "/home/horseman/nix-config/config/syncthing";
    overrideDevices = true;
    overrideFolders = true;
    settings = {
      devices = {
        "luna" = { id = config.sops.secrets."syncthing/luna"; };
        "terra" = { id = config.sops.secrets."syncthing/terra"; };
      };
      folders = {
        "Documents" = {
          path = "/home/horseman/Documents";
          devices = [ "terra" "luna" ];
        };
        "Programming" = {
          path = "/home/horseman/Programming";
          devices = [ "terra" "luna" ];
        };
      };
      gui = {
        user = config.sops.secrets."syncthing/gui_user";
        password = config.sops.secrets."syncthing/gui_password";
      };
    };
  };

When I run sudo nixos-rebuild switch:

error: A definition for option `services.syncthing.settings.devices.terra.id' is not of type `string'. Definition values:
       - In `/nix/store/z1w6lbli6y1yj0vhwvm0gq13ganifflz-source/machines/common/configuration.nix':
           {
             format = "yaml";
             group = "users";
             key = "syncthing/terra";
             mode = "0400";

This suggests that the secrets aren't import as string but rather as the secret object. I want to get the raw secret string that's in secrets.yaml. How? I've looked in the documentation here, but cannot find it.