Well, I decommissioned the server. Then I reinstalled it again (same server, same name, same IPs) and added it to Enhance cluster.
Now it doesn't show on the cluster. Maybe because it's the same machine.
@Adam what do I do? Reinstall the server again, give it a different name and add it to enhance cluster? Or this issue is because it's the same IP addresses?
I can't delete the current one because it has websites with it...
Thanks and sorry OP for taking the thread.