subscription in Graphql shutting down

I have a graphQL api I am trying to query .
I added a server side function :

 public class Subscription1
 {
     [SubscribeAndResolve]
     [Topic]
     [UseDbContext(typeof(ApplicationDbContext))]
     public IQueryable<Alert> OnAlertAdded([Service] ApplicationDbContext context, int clientId)
     {
         return context.AlertClients
             .Where(ac => ac.ClientId == clientId)
             .Select(ac => ac.Alert)
             .AsQueryable();
     }
 }

and I am using postman to get the data :

subscription OnAlertAdded {
    onAlertAdded(clientId: 1) {
        id
        name
    }
}

the problem is that the function returns all the alerts that belong to client id =1 but then then I see in postman logs WebSocket disconencted error 1006 and Operation completed .

I subscriptions that once called should query in a loop and never hung and everytime the server adds new alert the clients should be notified – at least this is what I was trying to achieve .

Is there any way I can get my code to work this way ? (listen constanatly and be notified by server changes )

Thanks so much!