This may point you in the right direction:

First the stored procedure I created for testing this which accepts @MyParameter as nvarchar(max) type.

IF OBJECT_ID('MH_TEST') IS NOT NULL

DROP PROCEDURE dbo.MH_TEST

GO

CREATE PROCEDURE MH_TEST

@MyParameter NVARCHAR(MAX)

AS

BEGIN

DECLARE @SomeValue BIGINT = 12345

SELECT @SomeValue AS ThisWasReturned

RETURN

END

GO

The procedure runs and the final part simply selects @SomeValue

Now for the package

Set the ExecuteSqlTask to return a single value result set. (Package_3.jpg)

Set up the ExecuteSqlTask the execute the stored procedure but use an expression to build the command to take into account the variable within the SSIS package you want to pass to the stored procedure (Package_1.jpg)

Set the result set (Package_2.jpg)

Run the package and you should see a message pop up showing what was returned from the SP (Package_4.jpg)

Any help?