Visited on May 20 without charging.
The charger is in the outdoor parking. 2h free with blue disc. It says "Privat", I assume that's because it's for the bank and other businesses in that building(?). The charger is probably for everyone though.
There are 2 additional chargers next to the Ost-mobil station, but there aren't any stickers on them to explain how they work. Maybe they are for private bank vehicles? It's not well explained at all.