I have created a simple application based on your C# code.

https://github.com/EiffelNETCore/examples/tree/main/web_apis/base_tester

At the moment DbC on .NetCore is not working.

If you have questions/suggestion about the examples,  use the github project 
so we can improve the code and the documentation.

>In https://github.com/EiffelNETCore/examples/tree/main/web_apis/my_first_api
>Compiling the Facade Library
>Navigate to the cs\asp_net_util folder.
>Execute the following command:
>dotnet build --output ..\..\..\my_first_api\packages

>This doesn't work.

I have fix the documentation, there was an issue in the path.