Hi! Thanks for replay.
This is the different case. I have a WordPress instance (Administration panel) on different URL address than frontend. For example:
The WP-Admin Url is cms.domain.pl
The Frontend address is domian.pl
WordPress allow to configure this by set accurate addresses in Settings->General.
But your plugin redirect user (after login to cms.domain.pl) to domain.pl/404 insted of cms.domain.pl/wp-admin/