NixOps error: "lacks a valid signature"

I’m trying to deploy a nixops configuration to a newly imaged raspberry pi, using nixops_unstable in 22.05.

The nixops documentation is… thin… to say the least.
I’ve come across an issue that I think requires modification of the nix config:

error: cannot add path '/nix/store/g3hch73lav78ag3k9lijbc50c89w0p61-nixos-manual-html' because it lacks a valid signature

I believe it may be because the vanilla image doesnt have the nixos user as a “nix.trustedUsers”.
Relevant discussion here

So I have my full declarative configuration that I cannot deploy.
And the image that has a mystery configuration, that I want to modify.

I’ve run nixos-generate-config but I just gives you a barebones configuration.
I believe if I were to run this, I would remove/destroy a fair chunk of configuration.

Is there a way to just apply a configuration delta to nix? Ie, add “nixos” to trustedUsers, but do nothing else?
Or am I on a completely wrong track?

It seems this is a nixops 2 issue.
Reverting from nixops_unstable to nixops resolved this for me.