Azure Log Analytics Workspace Request Forbidden

I am trying to send logs from my application to an Azure Log Analytics Workspace, in order to do that I develop the following code based on what I found in https://docs.microsoft.com/en-us/azure/azure-monitor/logs/data-collector-api

using maintenance.messaging;
using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
namespace maintenance.dataaccessobjects
{
    public class LogAnalyticsWorkspaceDAO
    {
        private static LogAnalyticsWorkspaceDAO _Instance { get; set; }
        private String WorkspaceId { get; set; } = AzureKeyVaultDAO.Instance.GetSecret("WorkspaceId"); //Get WorkspaceId from KeyVault
        private String SharedKey { get; set; } = AzureKeyVaultDAO.Instance.GetSecret("SharedKey"); //Get SharedKey from KeyVault
        private String ApiVersion { get; set; } = AzureKeyVaultDAO.Instance.GetSecret("LAWApiVersion"); //Get API Version from KeyVault 2016-04-01
        private String LogType { get; set; } = AzureKeyVaultDAO.Instance.GetSecret("LogType"); //Get LogType from KeyVault ApplicationLog
        private LogAnalyticsWorkspaceDAO()
        {
        }
        public static LogAnalyticsWorkspaceDAO Instance
        {
            get
            {
                if (_Instance == null)
                {
                    _Instance = new LogAnalyticsWorkspaceDAO();
                }
                return _Instance;
            }
        }
        private string GetSignature(String Method, Int32 ContentLength, String ContentType, DateTime Date, String Resource)
        {
            string Message = $"{Method}\n{ContentLength}\n{ContentType}\nx-ms-date:{Date}\n{Resource}";
            byte[] Bytes = Encoding.UTF8.GetBytes(Message);
            HMACSHA256 Encryptor = new HMACSHA256(Convert.FromBase64String(SharedKey));
            return $"SharedKey {WorkspaceId}:{Convert.ToBase64String(Encryptor.ComputeHash(Bytes))}";
        }
        public async Task<String> Post(String Message)
        {
            DateTime Date = DateTime.UtcNow;
            Dictionary<String, String> Headers = new Dictionary<String, String>();
            MessageSender MessageSender = new MessageSender(new Uri($"https://{WorkspaceId}.ods.opinsights.azure.com/api/logs?api-version={ApiVersion}"));
            Headers.Add("Method", "POST");
            Headers.Add("Log-Type", LogType);
            Headers.Add("x-ms-date", Date.ToString("r"));
            Headers.Add("Authorization", GetSignature("POST", Message.Length, "application/json", Date, "/api/logs"));
            return await MessageSender.Post(MessageSender.Message(Headers, Message));
        }
    }
}
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
namespace maintenance.messaging
{
    public class MessageSender : IDisposable
    {
        private readonly HttpClient Client;
        private Uri Url { get; set; }
        public MessageSender(Uri Url)
        {
            this.Client = new HttpClient();
            this.Url = Url;
        }
        public HttpRequestMessage Message(Dictionary<String, String> Headers, String Message)
        {
            HttpRequestMessage Request = new HttpRequestMessage(HttpMethod.Post, this.Url);
            Request.Content = new StringContent(Message, Encoding.UTF8, "application/json");
            foreach (KeyValuePair<String, String> Header in Headers)
            {
                Request.Headers.Add(Header.Key, Header.Value);
            }
            return Request;
        }
        public async Task<String> Post(HttpRequestMessage Request)
        {
            HttpResponseMessage Response = await Client.SendAsync(Request);
            Response.EnsureSuccessStatusCode();
            return await Response.Content.ReadAsStringAsync();
        }
        public void Dispose()
        {
            Client?.Dispose();
        }
    }
}

However I always fall under a 403 Forbiden, I guess the error should be in the Authorization header (Signature generation)
Do you know what I am missing? I tried looking for other signature generations but didn't find anything new

I may be wrong, but as far as I can see SharedKey is not Base64 encoded, so I just try with

HMACSHA256 Encryptor = new HMACSHA256(Encoding.UTF8.GetBytes(SharedKey));

But get the same error 403 Forbidden