Microsoft prepared quite good instruction how to install dotnet runtime on Linux. I’ve been interested in Debian distro. So I went pretty smooth through the first part of the manual (system setup). However installing dotnet I had constinously an error that package cannot be found. First comment: the package name has been changed and it is different for old versions and different for new ones (I did not investigated when it was changed, however for 2.0.7 it was old one, for 2.2.2 it is different).
The faulty part was missing package which was not present on clean system. So before you will try to install dotnet, check if you have apt-transport-https package.
sudo apt-get install apt-transport-https