Converting Javascript API Post request code to C#

I want to convert my javascript code to C#, I’m confused with the content-type of the header as application/json and the body as urlencoded, Please can anyone help me with converting this request to C#, thank you.

const echoPostRequest = {
  url: 'https://'+ pm.environment.get('apigw') +'/token',
  method: 'POST',
  header: 'Content-Type:application/json',
  header: 'Authorization: Basic '+ base64EncodedPassword,
 body: {
          mode: 'urlencoded',
          urlencoded: [
            {key: "grant_type", value: "client_credentials", disabled: false},
            {key: "scope", value: "scope_test", disabled: false}
        ]
      }
};

I tried this code below, is it correct ?

//This code is just for generating a base-64 code from a string
            string basicToken = ClientID+ ":" +ClientSecret;
            var basicBytes = System.Text.Encoding.UTF8.GetBytes(basicToken);
            string basic = Convert.ToBase64String(basicBytes);
//this is the rest api call
HttpClient client = new HttpClient();
            client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", basic);
            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, TokenUri);

            var postData = new
            {
                    grant_type= "client_credentials",
                    scope= "scope-test"
                
            };

            var content = new StringContent(JsonConvert.SerializeObject(postData), Encoding.UTF8, "application/x-www-form-urlencoded");
            request.Content = content;
            var response = await client.SendAsync(request);