Unable to send email from C# using WebClient

Unable to send email from C# using WebClient

Hi,  i am unable to send email for my C# code, although it was working previously and even i am able to send email from PostMan but when the same json is passed from C# code using WebClient it says Forbidden eveytime. Below given is my code snippet.

Note: Authorization token is generated for email gievn in FromAddress and same is used to get the AccountId using http://mail.zoho.com/api/accounts endpoint.
URL : https://mail.zoho.com/api/accounts/<accountId>/messages

public static Status SendEmail(ComposeEmail objEmail)
        {
            Status response = new Status();
            string methodUrl = string.Empty;
            methodUrl = ConfigurationManager.AppSettings["SMTPURL"];

            string json_data = string.Empty;
            ComposeEmail obj = objEmail;
            obj.fromAddress = ConfigurationManager.AppSettings["supportEmail"];
            obj.toAddress = objEmail.toAddress;
            obj.ccAddress = "";
            obj.bccAddress = "";
            obj.subject = objEmail.subject;
            string message = "Dear "+objEmail.Name+" <br><br>";
            message = message + objEmail.content;
            message = message + "<br><br>Regards <br>eSawari Team";
            obj.content = message;
            obj.mailFormat = "html";
            obj.encoding = "UTF-8";

            object toReturn = new object();
            //converting request into JSON string
            var requestJSON = JsonConvert.SerializeObject(obj);

            using (var client = new WebClient())
            {
                
                client.Headers.Add("Content-Type", "application/json");
                client.Headers.Add("Accept", "application/json");
                client.Headers.Add("Authorization", ConfigurationManager.AppSettings["EmailAuth"].ToString());
                try
                {
                    json_data = client.UploadString(methodUrl, HttpMethod.Post.ToString(), requestJSON);
                    response.Code = HttpStatusCode.OK;
                    response.Message = "Successful";
                }
                catch (System.Net.WebException ex)
                {
                    response.Code = ((System.Net.HttpWebResponse)(ex.Response)).StatusCode;
                    response.Message = ((System.Net.HttpWebResponse)(ex.Response)).StatusDescription;
                }
                catch (Exception ex)
                {
                    response.Code = HttpStatusCode.InternalServerError;
                    response.Message = ex.Message;
                }
            }
            return response;
        }