Install libappindicator3-0.1-cil-dev by entering the following commands in the terminal:
sudo apt update sudo apt install libappindicator3-0.1-cil-dev
Description:
CLI binding for libappindicator3 using GObject introspection
appindicator3-sharp assembly allows CLI (.NET) programs to use the Appindicator3 library. . This package contains development files for Appindicator# and should be used for compilation.
Homepage: https://github.com/stsundermann/appindicator-sharp/
Version: 12.10.0+git20151221-3
Section: universe/cli-mono