How to save image via url from xml file C#

Question

I am a newbie for c# I want to know how I download images by URL in my XML file. Now, I am writing the code for reading XML

using (XmlReader xmlReader = XmlReader.Create(pathXml))
            {
                while (xmlReader.Read())
                {
                    if (xmlReader.IsStartElement())
                    {
                        switch (xmlReader.Name)
                        {
                            
                            case "id":
                                string id = xmlReader.ReadString();
                                Console.WriteLine("id "+id);
                                break;
                            case "url":
                                string url = xmlReader.ReadString();
                                Console.WriteLine("url "+url);
                                break;
                        }
                        
                    }
                    
                }

Add more detail after trying to do but I am stuck again

using (MemoryStream mem = new MemoryStream(data))
                {
                    
                    using (var yourImage = Image.FromStream(mem))
                    {
                        yourImage.Save("Image2.png", ImageFormat.Png);
                    }
                }

in line using(var yourImage = Image.FromStream(mem)) it's show Exception Unhandled System.ArgumentException: 'Parameter is not valid' What should I do ?? Please help me

FYI: the URL in data is an image without format in Website that must be log-in user and password