Short Walks: 406 Error While Creating a .NET Core API

I’m afraid this is another of those: “What has AddMvc() ever done for us" posts. Today, I was creating a brand new .NET Core 2.1 API and, instead of calling AddMvc in ConfigureServices, I instead used AddMvcCore:
public void ConfigureServices(IServiceCollection services)
When I tried to access the API, I got a 406 error. The fix is very simple (and one that using AddMvc()  does for you: