Visited yesterday without charging.
It's not clear who can charge here. The sign at the entrance says "P Besucher Stoffel Mels". There's a series of parking spots in the gravel. The 2 spots in front of the charger were free but not indicated any differently, except the far right spot with a sign "Besucherparkplatz Uptown Mels"
In any case, there's no parking meter or maximum time posted.