The type or namespace name 'Citrusresponse' could not be found (are you missing a using directive or an assembly reference?

Question

I am working on an ASP.NET website and using Citrus pay framework. I am Getting error on this line in my code:

Citrusresponse s = DB.GetCollection<Citrusresponse>().FindOneById(TransID);

Here are the total modules that I am using in my code.

using MongoDB;
using CitrusPay;
using MongoDB.Bson;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

I am struggling since two days find the solution of this but still no bug. I have gone through the community forum and questions here.

If you be great anyone can help me in figuring out this bug.

Let me know if you need more information.