Maybe it's security settings from my company.
It's not a security setting. The web applications are hosted on your machine. Plus, a 404 mean the client was able to access the remote web application because the web application returned a 404 to the client.
One last screenshot. Do you see anything?
A 404 simply means the URL was not found. The screenshot you shared is a web application not Web API. Did you add Web API support to an MVC or Razor Pages application? Can you share your route setup in the Startup.cs or Program.cs files? There are several different port numbers in your post. Are you sure port 44347 hosts the API?
After reviewing your code, it seems to me the problems you are experiencing stem from not understanding fundamentals. I provided links to two Web API tutorials. I also provided a link on routing. Did you go through the tutorials? I'm asking because the tutorial cover the very aspects you are struggling with.
Before you argue that the tutorials use JSON not XML, the data format does not matter. As already illustrated in this thread, serialization is a configuration. Web API handles JSON by default but can also handle only XML or JSON and XML at the same time.