C# SSO call gives 400 when I try to get a token

[Tanaka_Seiko]

Hey guys,

I am stuck here. This should work, but I get a http 400 instead of a token. I really ould like to work through this and understand the mechanics myslef instead of using a library. Do i do anything wrong here? See code:

 private void GetToken(String codeStr)
    {
        WebClient request = new WebClient();
                             
        string auth_header = $"{clientID}:{secretKey}";
        string auth_header_64 = $"Basic {Convert.ToBase64String(Encoding.UTF8.GetBytes(auth_header))}";
        request.Headers[HttpRequestHeader.Authorization] = auth_header_64;
        var post_params = new NameValueCollection();
        post_params.Add("grant_type", "authorization_code");
        post_params.Add("code", codeStr);

        byte[] response = request.UploadValues($"https://login.eveonline.com/oauth/token", "POST", post_params);
        string actual_response = Encoding.UTF8.GetString(response);

        MessageBox.Show(actual_response);
    }

[Blacksmoke16]

Try setting a Content-Type: application/x-www-form-urlencoded header and making sure your values are properly escaped.

Also, whats the error you get back?