I have recently installed Leaf Spy on a Samsung Note 5 after testing it first on my android tablet. I connected it to Dropbox first on my tablet. I know it worked because the Leaf Spy folders were created on Dropbox, but no files have been synced there.
When I start the app on my Note 5, I get the message "Warning. Disabling Dropbox." No amount of checking and unchecking the option in settings will cause the Dropbox Authorization window to be displayed.