Kubectl - Unable to connect to the server: Service Unavailable

Hi,
i’m starting using Kubernetes, after installed it on a little cluster, i have reboot the node (manager).
After the reboot, every time i try to execute a command using “kubectl” it gives me this error:

Kubectl Unable to connect to the server: Service Unavailable

how can i fix/debug the problem?

Cluster information:

bare-metal
Host OS: Centos 8