How to pass string values in clause in SQL?

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SQL

create PROCEDURE [dbo].[Sp_MultiSearchNews]
       @Topic		   VARCHAR(200) = NULL,
       @pageno		   int   = NULL,
       @pagesize	   int = NULL 
       AS
   BEGIN	  
        IF( @Topic = 'null' )
            BEGIN
                SET @Topic = NULL;
            END;    
        DECLARE @sql NVARCHAR(MAX), @sqlPaging NVARCHAR(MAX);
        SET @sql = 'select distinct NewsID,CompanyID,Companyname,NewsTopic,Topic from MulitSearch_PortalNews WHERE 1=1';        
        IF @Topic IS NOT NULL
        SET @sql = @sql + ' and Topic IN (' + @Topic + ')';
	   DECLARE @count VARCHAR(MAX);
        SET @count = 'select count(*) as TotalCount from ( ' + @sql + ' ) as T';        
	   exec (' select CAST(ROW_NUMBER() OVER(ORDER BY NewsID) AS INT) AS Row, TotalRecords,NewsID,CompanyID,Companyname,NewsTopic,Topic 
	   from ( SELECT ROW_NUMBER() OVER(ORDER BY NewsID ) AS Row,('+@count+') AS TotalRecords ,* from ( '+@sql+' ) as T ) as pageResult 
	   where ( Row between (('+@pageno+' -1)* '+@pagesize+'+1) AND '+@pageno+' * '+@pagesize+' )'  );
    END;

What I have tried:

1) MulitSearch_Portal is a views table(views)

Topic - field is string in my table saved in comma separated values.

If i run comment
--Sp_MultiSearchNews '371,382',1,20
Below error is accrued
Conversion failed when converting the varchar value '371,382' to data type int.

i tired - SET @Topic = REPLACE(@Topic , ',' , ''' , ''') its not work properly.

how to pass string values In clause using sql. Purpose of procedure need multisearch.
Kindly help please........