Apache Redirect Message

Hello Experts,

I am in the middle of setting up new website for our department and wished to know how we can redirect original website having same webaddress on a new server.

We have new website running on SLES 15 and Apache 2.4

So far I am able to setup the apache server and the new website works just fine. Lets say https://newaddress/subdir and it displays the contents correctly. Now I wish to setup a Redirect so that any clicks on the old website https://oldaddress/subdir will be redirected to a new ones with a Message (Popup or so) informing the users that there is now a new Website available.

For the redirection part i used .htaccess file and placed it in Quote:

/srv/www/htdocs

.htaccess -->

Quote:

<IfModule mod_rewrite.c> RewriteEngine on RewriteBase / RewriteRule ^(.*)$ https://newaddress/subdir/$1 [R=301,L] </IfModule>

It works so far. But the Popup window, is where I require mainly the guidance. So we should be setting up ErrorDocument for this?
Or is there any better way?

Thanx.

-Admin