After installing Multistore login plugin, you have to manage settings in NOP admin.
(path: Admin/MultistoreLogin/Configure).
Plugin enables multistore configuration - you can configure different settings for different stores if needed.
Require login - must be selected in case shop must be accessible only when logged in.
Login path  - Login redirect path if not logged in and logging in is required.
Allowed paths - Comma separated list of paths that are allowed even if logging in is required.