I can’t connect my C# Win Form app with MariaDB.

For litle context I need to deploy my C# Winform App. I success to create a setup.exe and now I need to deploy the DB. I have create a VPS and create the great database with a simple script SQL create by phpmyadmin. I’m almost sure that my connection string and connection credentials are OK

I use the extension MySQL Connector

Here my code :

private string connectionString = ConfigurationManager.ConnectionStrings["localhost"].ConnectionString;
            public string GetHashForAuthentification(string login_m)
            {
                string hash = null;
                using (MySqlConnection conn = new MySqlConnection(connectionString))
                {
                    conn.Open();
                    string query = "SELECT password_m FROM medecin WHERE login_m = @login_m;";
                    using (MySqlCommand command = new MySqlCommand(query, conn))
                    {
                        command.Parameters.AddWithValue("@login_m", login_m);
                        using (MySqlDataReader reader = command.ExecuteReader())
                        {
                            if (reader.Read())
                            {
                                hash = reader.GetString("password_m");
                            }
                        }
                    }
                    conn.Close();
                }
                return hash;
            }

When I try to login by the debug mode from Visual Studio, I have this error who spawn at “conn.Open()” : System.InvalidCastException: ‘Object cannot be cast from DBNull to other types.’

Have you some solution for my problem ? May be my MariaDB Version ?

Thanks…

I try to change the user of the database, try to change the connection string