To solve ignore what's currently written in the README, and modify as follows:

cd ExampleChatApplication
dotnet build ChatClient/ChatClient.csproj -f netcoreapp3.0 -c Release
dotnet build ChatServer/ChatServer.csproj -f netcoreapp3.0 -c Release

Run server in one terminal on default port with TLS support

dotnet exec ChatServer/bin/Release/netcoreapp3.0/ChatServer.dll --c ChatServer/server.pfx

Run client in another terminal

dotnet exec ChatClient/bin/Release/netcoreapp3.0/ChatClient.dll username 127.0.0.1/ChatClient

@tyranid It would be worth updatign the README fyi

from examplechatapplication.