SQL Server Stored Procedure.

Hi.
I am trying TO call this sp AND it dont EXECUTE the @sql STATEMENT, IF i look it IN watch its EMPTY. what could be the reaosn FOR it.

EXEC Update_Transaction  '22','0',0

CREATE PROCEDURE [dbo].[Update_Transaction]
    @TransactionEntryID INT ,
    @UserID INT ,
    @ID INT OUT
AS
    BEGIN

      DECLARE       @sql VARCHAR(max);

    SET NOCOUNT ON;
        IF @UserID = 0
            BEGIN

                SET @UserID = NULL;

            END
               
                  BEGIN            

SET @sql = 'INSERT  INTO + table1' +
                '( TransactionEntryID ,
                  UserID ,
               
                )
   VALUES ('+ cast(@TransactionEntryID as varchar(100))+', '+ cast(@UserID as varchar(100))   +')'

                                                       EXEC (@sql)
END      
    END