If the .htaccess file is not writable or you run a multisite WordPress, in order for Hide My Wp to work you need to write the code you receive in the Settings > Hide My Wp after you set and save the Ninja mode.

If you don’t have server access you can install a plugin that will help you with this:
https://wordpress.org/plugins/wp-htaccess-control/

You can remove the wp-htaccess-control plugin after you’re done with the setup.