Conversion failed when converting the varchar value to data type int

DECLARE
        @JOBTYPE INT,
        @JOBID INT,
        @SQL VARCHAR(2000),
        @CLIENTID INT,
        @BRANDCATEGORYID INT,
        @BRANDID INT
                        
        SET @JOBTYPE=2
        SET @JOBID=57032
        
        SELECT @JOBTYPE AS JOBTYPE,@JOBID AS JOBID              
        IF @JOBTYPE IN (2,5)
        BEGIN
                SELECT @CLIENTID=CAST(I.clientid AS INT),@BRANDCATEGORYID=CAST(M.brandcategoryid AS INT),
                @BRANDID=CAST(I.brandid AS INT)FROM tbl_iteration I
                INNER JOIN tbl_mechanicalbrief M ON M.mechanicalid = I.mechanicalid
                INNER JOIN tbl_client C ON C.clientid = M.clientid
                INNER JOIN tbl_brandcategory BC ON BC.brandcategoryid = M.brandcategoryid
                INNER JOIN tbl_brand B ON B.brandid = I.brandid
                WHERE I.iterationid = @JOBID
        END 
        
        SELECT @CLIENTID AS CLIENTID,@BRANDCATEGORYID AS BRANDCATEGORYID, @BRANDID AS BRANDID --THESE ARE ALL INTEGER VALUE
                        
        SET @SQL = 'select Q.noticeid clientname,brandcategoryname,brandname,comment from tbl_QCNotice Q
                                INNER JOIN tbl_client C on C.clientid = Q.clientid
                                LEFT OUTER JOIN tbl_brandcategory BC on BC.brandcategoryid = Q.brandcategoryid
                                LEFT OUTER JOIN tbl_brand B on B.brandid = Q.brandid '
        SELECT @SQL     --UPTO HERE ITS WORKING FINE
                                
        IF @CLIENTID <> 0
                SET @SQL = @SQL + ' WHERE Q.clientid IN (' + @CLIENTID + ')'
                
        SELECT @SQL     --HERE IT GIVES ERROR
        
        --IF @BRANDCATEGORYID <> 0 
        SET @SQL = @SQL + ' AND Q.brandcategoryid IN (0,'+ @BRANDCATEGORYID +')'                        
        SET @SQL = @SQL + ' AND Q.brandid IN (0,'+ @BRANDID +')'                
        SET @SQL = @SQL + ' ORDER BY noticeid DESC'     
                
        SELECT @SQL
        EXEC(@SQL)