[Wiring Help] ZBMiniL2 (Extreme) -not working right- Stair case 2-switch

It must be an older house then. Older hoses and apartments do not have neutral wires delivered to wall box. That used to be the standard for lighting. The same was in EU. But this is not the main problem.
You need to discover how many wires run between boxes. If there are only two, there’s no chance to utilise ZBMINI-L2 in your case. Read this thread.