Getting DropBox to work for Gemian is a pain as there is not an arm version and even if you choose to compile the install yourself from the DropBox site the helper agent it then wants to install is not binary compatible.
The workaround is to use the excellent Maestral:
https://github.com/SamSchott/maestralIt requires Python3 and pip to be pre-installed. You can check this:
which python3
and if not installed
sudo apt install python3
and then
sudo apt install python3-pip
Then to install Maestral:
python3 -m pip install --upgrade maestral
There is a GUI option but the pyQT5 libs are outdated and therefore it wont' satisfy the dependancies and install, however you can simply work with the command line version which works fine (see the site link above for how that works).
You can choose to have maestral start each time you start Gemian or just start it when you wish from the command line with 'maestral start' and check status with 'maestral status'
The config file lives at /home/cosmo/.config/maestral/maestral.ini