Imgur API upload image and retrieve URL to insert on an HTML variable

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C#

Hello,

I'm trying to use the url of the image uploaded to the imgur API service so it should look like this:

<img='_imgurl'>

This is the actual code I have, on which it gives me a error 404 or error 401, corresponding to "System.Net.WebException: 'The remote server returned an error: (404) Not found.'"

using (var w = new WebClient())
                {
                    using (var ms = new MemoryStream())
                    {

                        using (var image = Picture.Image)
                        {
                            using (MemoryStream m = new MemoryStream())
                            {
                                image.Save(m, image.RawFormat);
                                byte[] imageBytes = m.ToArray();

                                // Convert byte[] to Base64 String

                                string base64String = Convert.ToBase64String(imageBytes);
                                var values = new NameValueCollection
                                {
                                    { "key", "2781d465a48c3e2" },
                                    { "image", Convert.ToBase64String(imageBytes) }
                                };
                                byte[] response = w.UploadValues("https://api.imgur.com/3/upload", values);

                                var responseXml = XDocument.Load(new MemoryStream(response));
                                _imgurl = (string)responseXml.Root.Element("link");
                            }
                        }
                    }     
                }

What I have tried:

Changing the url and the key from client_key to secret_key
Tried the solution provided.
Tried to use the variety of links and diferent keys.(Gives me (401) error: Not authorized)