Linux BlueZ dbus communication
You have to activate the experimental features for your bluetooth set in order to get GATT services enabled.
On a Debian system you can achieve this by putting
NOPLUGIN_OPTION="-E"
into the /etc/default/bluetooth file.
After restart, in order to get my device (Logitech MX Master) working properly on my Debian Stretch, I also had to pair and trust it manually using the bluetoothctl command. I had no success with the graphical bluetooth tool from Gnome.