As for now, the development is paused. Currently the only way to "sync" is to export the database on one device, and import it on another.

We're looking for ways of implementing a proper sync though. Synching is not an easy problem, especially between different platforms. For example, Obsidian, who recently released a mobile app, states that "Currently, there is no known support for the following sync services on iOS yet: Dropbox, Google Drive, OneDrive, Syncthing" (https://help.obsidian.md/Obsidian/iOS+app). iCloud Drive seems to be a viable option, but I'm not sure it will work on Android.