Api error access denied

hi, Thank you for your feedback,

am still not sure what should be the loop URL, but I put it back as it is original shape , and I placed my App key instead of the "xxxxxxx", so I have the code header like that:

private const string ApiKey = @"xxxxxxxxxxx";
 
private const string LoopbackHost = "http://127.0.0.1:52475/";

  
private readonly Uri RedirectUri = new Uri(LoopbackHost + "AUTHORIZE"); 

// URL to receive access token from JS.
private readonly Uri JSRedirectUri = new Uri(LoopbackHost + "TOKEN");//

but I get the following we page result:

I'm not sure what do I miss, especially that I don't know where should I place the "App Secret"

please explain with more details if it is possible