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?