The first thing you need to do is confirm if your instance of PHP supports Redis. (That's separate from having Redis installed somewhere.)
You can do this by checking PHPInfo. There is a link to it in your ACP.
YOUDOMAIN.COM/admin/?app=core&module=support&controller=phpinfo
You should see something like:
If you don't see all that stuff (and only a few lines), it most likely means you need to have redis support compiled into PHP. This has been the most common issue that I've seen why Redis won't work for some folks.
Next... in your screenshot, you show a public IP in the server field. If Redis is hosted on a different physical server, you need to confirm that outbound TCP port 6379 (or whatever port is used by the Redis provider) is open on your server's firewall. Otherwise your server won't be able to reach the other server.
You also don't have a port number specified in your screenshot. You should most likely list it.
If Redis is running on the same server as your website, change server address to "localhost" or "127.0.0.1". Again, I would also specify the port Redis is listening on that server as well (or if it's running as a socket, you could provide the path to the socket file).
Finally... once it is actually all setup and working, it can take several minutes for that error to go away. Generally once it's actually working, it can take 3-5 minutes for that error to disappear.