Redirect module does not allow redirection for existing node's path alias I installed fresh Drupal 8 and after that the Redirect module with proper settings. After adding the redirect rule for a path alias it does not work but it saves data properly into the database.

But it works if I add internal path like node/{id}. In this case it works for internal path as well as path alias. 

I just wanted to redirect it on the basis of path alias only. Is it possible to add only path alias for the redirection?
I just ran into this also.  You may want to look at https://www.drupal.org/project/url_redirect to see if it fits your needs.