Realtime Subscriptions Not Receiving Updates

1. Table doesn't have realtime replication enabled in Supabase dashboard
2. Subscription set up after initial data load
3. Using .select() query that doesn't match subscription filter
4. Supabase JWT missing realtime permissions
5. WebSocket connection blocked by CORS or firewall

Enable realtime in Supabase dashboard > Table Editor > click table > Replication section.

Subscribe before loading data:

useEffect(() => {
  const subscription = supabase
    .from('messages')
    .on('*', (payload) => {
      setMessages(prev => [...prev, payload.new]);
    })
    .subscribe();
  
  return () => subscription.unsubscribe();
}, []);