Laravel - Notifications - Adding A Client Reference

If you would like to keep track of costs per user, team, or client, you may add a "client reference" to the notification. Vonage will allow you to generate reports using this client reference so that you can better understand a particular customer's SMS usage. The client reference can be any string up to 40 characters:

     * Get the Vonage / SMS representation of the notification.
     * @param  mixed  $notifiable
     * @return NexmoMessage
    public function toNexmo($notifiable)
        return (new NexmoMessage)
                    ->clientReference((string) $notifiable->id)
                    ->content('Your SMS message content');