Supabase Realtime Subscription Not Updating in Real-Time

1. Replication not enabled for table in Supabase dashboard
2. Subscription not properly set up or connected before data changes occur
3. Cleanup (unsubscribe) happening too early or not at all, causing memory leaks
4. Database changes made with direct SQL, bypassing replication triggers
5. Realtime configuration not loading or URL incorrect

Enable replication: In Supabase dashboard, go to Replication > select table > enable replication. Realtime only works for replicated tables.

Proper subscription: Use on().subscribe() and clean up in useEffect cleanup:
const sub = supabase.on('postgres_changes', {...}).subscribe()
return () => sub.unsubscribe()

Verify auth: User must be authenticated or have anon access to table RLS policies for realtime to work.

Test connection: Check Supabase project Status page for realtime service health. Check browser DevTools for WebSocket connection.