setting up backendless for web api .net

I've declared this in my program.cs

public class Program
    {
        public static void Main(string[] args)
        {
            NewMethod();
            CreateHostBuilder(args).Build().Run();


        }

        private static void NewMethod()
        {
            Backendless.InitApp("53D6D975-0E31-9690-FFA8-508CD4FB5D00", "60CE8F1D-15ED-F9DE-FFCC-B4FEDB0EF100");
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

In return i get this error

System.IO.FileNotFoundException
  HResult=0x80070002
  Message=Could not load file or assembly 'EngineIoClientDotNet, Version=1.0.7.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.
  Source=Backendless
  StackTrace:
   at BackendlessAPI.Backendless.InitApp(String applicationId, String apiKey)
   at WebApplication2.Program.NewMethod() in C:\Users\Popsh\source\repos\WebApplication2\WebApplication2\Program.cs:line 27
   at WebApplication2.Program.Main(String[] args) in C:\Users\Popsh\source\repos\WebApplication2\WebApplication2\Program.cs:line 19