calling extension methods and calling them in data contracts

I have using a 3 party payment cart provided by chase.
below is a extension method. Irequest is the object provided by chase for sending them a request.
String ordernumber is anything string.

Suppose , i want to call this SetMerchantOrderNumber(this IRequest request, string orderNumber)  in another class, how do i call it. i know i have to using this class using using in class file.

also, how do i mport this into datacontracts for sending the request to chase using wcf.
using System;
using System.Collections.Generic;
using System.Linq;
using ChasePaymentech.Spectrum;
using Vertrue.Core.String;
using Vertrue.Core.PaymenTech.Exceptions;
using Vertrue.Core.PaymenTech.Extensions.CreditCardVendors;
using Vertrue.Core.PaymenTech.Interfaces;

namespace Vertrue.Core.PaymenTech.Extensions.Request
    public static class IRequestExtensions
        /// <summary>
        /// Validates the value passed in does not contain invalid characters and sets the MerchantOrderNumber property on the request.
        /// </summary>
        /// <param name="request">Any Paymentech request.</param>
        /// <param name="orderNumber">A string value must not contaion |,^,%,\,/,[,],`,~ characters and must be less than 23 characters.</param>
        public static void SetMerchantOrderNumber(this IRequest request, string orderNumber)
            if (!string.IsNullOrWhiteSpace(orderNumber))
                var invalidCharacters = new HashSet<char> { '|', '^', '%', '\\', '/', '[', ']', '~', '`' };
                const int merchantOrderNumbermaxLength = 22;

                //check for invalid characters
                if (orderNumber.ToCharArray().Any(invalidCharacters.Contains))
                    throw new ArgumentContainsInvalidCharacterException("value", invalidCharacters);

                //check for invalid length
                if (!orderNumber.IsValidLength(merchantOrderNumbermaxLength))
                    throw new ArgumentToLongException("value", merchantOrderNumbermaxLength);

                //should be left aligned and padded with spaces.
                orderNumber = orderNumber.Trim().Length == 0 ? null : orderNumber.PadRight(22, ' ');
                orderNumber = null;

            const string merchantOrderNumberKey = "MerchantOrderNumber";
            request[merchantOrderNumberKey] = orderNumber;
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käµfm³d 👽Commented:
You would call it as:
IRequest someRequest = new IRequest();  // I know this isn't correct and is only for illustration


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DattuAuthor Commented:
i am looking for the exact syntax, pleasee....
Irequest is an interface.
if you want to access the extension you need to have the implementation of IRequest.
for e.g

namespace MyInterface
    interface IRequest
        string DoRequest();
    public class Request : IRequest
        #region IRequest Members

        public string DoRequest()
            return "Welcome";


using MyInterface;

namespace MyExtensions
    static class MyExtension
        public static string ExtendMe(this IRequest req, string name)
            string test = req.DoRequest();
            return test + " " + name;

usage in other classes
using MyInterface;
using MyExtensions

  IRequest myReq = new Request();

this will output Welcome, Tom.

I hope that this helps you

Thanks and regards,
käµfm³d 👽Commented:
>>   i am looking for the exact syntax, pleasee....

I gave you the syntax in line 3 of my post. You asked for the syntax to call an extension method, not how to declare an interface. And I stated in my post that the variable declaration was not proper.

To make the declaration proper, set it equal to a new instance of any class which implements IRequest.
DattuAuthor Commented:
Sorry, it tok me so long to close this questiona and had to give points to both of you. I wish I give each of you 250 points. Sorry again for the delay.
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