The remote server returned an error: (403) Forbidden in WebRequest.GetResponse Method for some url's

Question

Am using WebRequest to validate Url before saving it to Db, But for some url's am getting 403 forbidden error. Please suggest me how can i resolve this issue or any alternate way for this.

i have used code like below.

var webRequest = WebRequest.Create(url);
var webResponse = webRequest.GetResponse();

i also tried WebClient in local its working but when we deploy its throwing same error. Please find the WebClient code aswell

 using (WebClient webClient = new WebClient())
 {
    webClient.Headers.Add("user-agent", "test");
    string content = webClient.DownloadString(url);
 }  

The main purpose we are used this to check when user enters any url attacks.. Please suggent if any way to resolve this