bartthe1st

Thank you Chad!

If anybody is interested as well:
I created a functions.php in my child-theme-folder and added:

<?php
// Redirects specified url to the login page.
/*
 * This example makes use of wpmem_current_url() to get the url of the 
 * page the user is currently requesting. See documentation here:
 * https://rocketgeek.com/plugins/wp-members/docs/api-functions/wpmem_current_url/
 */
add_action( 'template_redirect', 'my_redirect_to_login' );
function my_redirect_to_login() {
  if ( ! is_user_logged_in() && wpmem_current_url() == site_url( '/pagename/' ) ) {
	  wpmem_redirect_to_login();
  }
  elseif ( ! is_user_logged_in() && wpmem_current_url() == is_single() ) {
  	wpmem_redirect_to_login();
  }
  return;
}

Now the redirect is supposed to be in action, if the user is not logged in and wants to access the page “pagename” or any blog post.