I get an error (400) when I attempt to test SimpleTest example from Sdk-dotnet from this Link
on my machine (Windows 10 32bit 1909) Visual Studio 2015.
I followed all instructions.
Here is my App Console:
App Console
Here is the Code:
// This loopback host is for demo purpose. If this port is not
// available on your machine you need to update this URL with an unused port.
private const string LoopbackHost = "http://127.0.0.1:52475/";
When I run the project I get this

I click (N) or (Y) or (Enter), I get this
https://www.dropbox.com/oauth2/authorize?response_type=token&client_id=<MADE_IT_HIDDEN>&redirect_uri=http:%2F%2F127.0.0.1:52475%2Fauthorize&state=35d21a9368224dbcb2f61bb5d2705a74

I have IIS installed and working.
I registered the port 52475 and made sure it is unused, like this
