kubectl not able to pull the image from private repository

You need to refer to the secret you have just created from the Pod definition.

When you create the secret with kubectl create secret docker-registry my-secret --docker-server=123.456.789.0 ... the server must exactly match what's in your Pod definition - including the port number (and if it's a secure one then it also must match up with the docker command line in systemd).

Also, the secret must be in the same namespace where you are creating your Pod, but that seems to be in order.