Thanks for your reply and adding the noSQL licence, @CraigWeb!
Regarding the other error: I wanted to migrate existing H2 data into noSQL and was mislead by the documentation:
The NoSQL migration can take several hours to complete but it will happen in the background.
My bad -- I thought it was a one-click solution given, that Mango knows which DB it is using and what the credentials are. Will report back when I had access to the client's server again. Thanks again for your help!