When filtering charger networks you can choose Mer and select your preference. For demonstration purpose, choose only. In route planning Mer isn't available at all and a longer route will fail because no charger is available.
If you select a known charger location it is marked with Mer's previous name, Bee (charging solutions). But Bee isn't available as a filter item. So there is no way to select your preference for Mer as of now.
I can confirm it works for me as well now. Thank you!
I tested to plan a route only using Mer chargers and it seemed to work fine. The chargers will appear with both Mer and name and the old name. Maybe this is a change since you asked so want to check if this is working for you now and we can close the ticket. If you still are facing issues I would be happy to help promptly.