Protonvpn-gui :: Unknown API error

Has anyone recently had any luck running the official ProtonVPN GUI on NixOS?

I see that another NixOS user reported it was working back in 2022. However, when I try, I get “Unknown API error” (when I press the Login button).

Searching for this error, it seems to have been a known problem in the past. So, I also tried installing the unstable version. However, trying to run the unstable package, I get:

RuntimeError: The Secret Service daemon is neither running not activatable through D-Bus