How can I use order by in dynamic query?

Question

Hello everyone,

From this below query, Order by can not working when I am passing parameter @SortColumn. But it working directly passing value. For eg, if I am giving AgencyName asc instead of @SortColumn. Its working fine. How to solve this issue when I am passing parameter?

DECLARE @StartRowNum varchar(10)
DECLARE @EndRowNum varchar(10)
DECLARE @SortColumn varchar(100)
DECLARE @TransId varchar(100)

SET @SortColumn = 'AgencyName asc'
SET @TransId = 1481143433
SET @EndRowNum = 50
SET @StartRowNum = 0

begin

select  ROW_NUMBER() over (order by @SortColumn )  AS RowNum, tempID,ProgramId,ChannelId,Date_DL,StartTime,EndTime,Viewers,
  Tx,TVR,CVR,DVR,
  Details_Id,
   MastersId,BrandsId,ItemsId,Note,PaidForOrProp,Verbal,Indexes,Seconds,
     GradesId,ChannelName,CountryName,WebSiteName,ProductionName,BrandName,ItemName,
     Product_company_id,CompanyName,ProductGroupsId,
     SectorsId,SubSectoresId,AgenciesId,GroupName,SectorName,SubsectoreName,
     AgencyName,agencyID,QualityGrade,CPH_DL,CPH_UN,Country_CPH,Country_UN,
     Web_CPH,Web_UN,
 AdFactor,Duration_Factor,DaypartName,DaypartId,DaypartFactor,CinemaFactor,DigitalFactor,MediaValue from
 dbo.MonitorExposureFinal WHERE Trans_Id = @TransId
 end