How to save edits in .mm mindmaps?

Hi, I’m new to the NC universe.

My collegues and I would like to edit .mm mindmaps online which I’ve created with Freeplane. For that I’ve tried the files_mindmap app. At first I was very impressed because If I clicked on a .mm file in the file listing the mindmap will be opened. Also I could edit the mindmap. But within closing no changes will be saved.

Does anyone know a workaround e.g. a converter from .mm to .km?

Regards, Andreas