Get OAuth 2.0 access token of Paypal using HttpClient in c#

Here called paypal Rest API using System.Net.Http.HttpClient for OAuth 2.0 access token

try
 {
// ClientId of your Paypal app API
        string APIClientId = "ASCxaD7FzuvGbX-xxxxxxxx.....xxxxxxxxxxx-6RZDgwLuOyrCsy3";
               
// secret key of you Paypal app API
string APISecret = "ENldyFXuW46R7Wv0xxxxxxxx.....xxxxxxxxxxxee8pyH8";

        using (var client = new System.Net.Http.HttpClient())
        {
            var byteArray = Encoding.UTF8.GetBytes(APIClientId+ ":" + APISecret );

            client.DefaultRequestHeaders.Authorization = new Headers.AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));

            var url = new Uri("https://api.sandbox.paypal.com/v1/oauth2/token", UriKind.Absolute);

            client.DefaultRequestHeaders.IfModifiedSince = DateTime.UtcNow;

            var requestParams = new List<KeyValuePair<string, string>>
                                {
                                    new KeyValuePair<string, string>("grant_type", "client_credentials")
                                };

            var content = new FormUrlEncodedContent(requestParams);
            var webresponse = await client.PostAsync(url, content);
            var resp = await webresponse.Content.ReadAsStringAsync();

// response will deserialized using Jsonconver
            //return JsonConvert.DeserializeObject<PayPalGetTokenResponse>(resp);
        }
    }
    catch (System.Exception ex)
    {

    }