Function import in dynamic store procedure

I have a store procedure with dynamic query. I am passing the column name in a variable and getting the result. Here is the store procedure.

ALTER PROCEDURE [dbo].[prosperGetSampleResults]
	@TestId varchar(200),
	@TestSeriesId varchar(200),
	@ColName varchar(128)
AS

if @TestId is null
begin
  set @TestId = 73
end

if @TestSeriesId is null
begin
  set @TestId = 1005
end

if @ColName is null
begin
  set @ColName = 'Gloss60'
end

BEGIN
	DECLARE @FMTONLY BIT;
	 IF 1 = 0
	 BEGIN
	  SET @FMTONLY = 1;
	  SET FMTONLY OFF;
	 END

	SET NOCOUNT ON;
	declare @sql nvarchar(max)
 select @sql = 'SELECT T.TestSeriesSampleId
 ,SS.TestSeriesId,T.TestId,SS.TestSeriesSampleCode,S.TestDescription,T.[Standard],R.ExposureTime,R.TotalExposureTime,R.' + @ColName+'
  as Result from TestSeriesSampleTesting T

 inner join TestSeriesSampleResults R
 on T.TestSeriesSampleId = R.TestSeriesSampleId

 inner join TestSeriesSample SS
 on SS.TestSeriesSampleId = T.TestSeriesSampleId

 inner join Test S
 on S.TestId = T.TestId and T.TestId = ' +@TestId+'
 and SS.TestSeriesId = '+ @TestSeriesId

	SET FMTONLY OFF;

  exec sp_executesql @sql

  IF @FMTONLY = 1
  BEGIN
  SET FMTONLY ON;
 END

END

 

Now in entity framework when I am trying to add function import, the complex query is disabled and no result is coming clicking on 'Get Column Information' button. Please help how to solve the problem.