Authentication required when making requests from different contexts

I use FlightXML3, and it works perfectly when I make requests using Postman REST Client on desktop.
However, when I make the requests in my C# console application or other mobile REST Client I receive the response “Authentication required”.
Clearly I use the correct keys etc, since it is the exact same request I execute.
Why do I receive this response?

Fixed. The .NET WebRequest could not interpret the example URL from FlightXML3 documentation. (Username:api-key@…)
I had to set it explicitly as Basic authentication.

Did you look at our example code from flightxml3_examples/dotnet/rest/dotnetcore at master · flightaware/flightxml3_examples · GitHub ? Do you have any suggested changes for our example?