Failed to add custom plugin to oh-my-zsh terminal

Question

I want to add a new custom plugin to my oh-my-zsh terminal
I created a new directory under ~/.oh-my-zsh/custom/plugins/disable_gke_tunnel.
Added a new file named disable_gke_tunnel.plugin.zsh

disable_gke_tunnel.plugin.zsh:

disable_gke_tunnel() {
  echo "Disabling active GKE tunnel and aliases"
  alias k='kubectl'
  unalias helm > /dev/null 2>&1
  unalias kubens > /dev/null 2>&1
  ssh -S /tmp/sslsock -O exit gke-mgmt > /dev/null 2>&1
  if [ $? -eq 0 ]; then
    echo "GKE tunnel closed successfully."
  else
    echo "Failed to close GKE tunnel."
  fi

  echo "Done!"
}

I added this plugin to the list of plugins under .zshrc

plugins=(
    git 
    web-search 
    terraform 
    sudo 
    copyfile 
    copypath 
    gcloud
    zsh-autosuggestions
    history
    gke-tunnel
    disable-gke-tunnel
)

Now when I execute the command source ~/.zshrc I get this error:
[oh-my-zsh] plugin 'disable-gke-tunnel' not found

What am I missing ?