How To Test Stored Procedure With Output Parameters In Management Studio

I have this SP:

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[GetSessionInformation]
@CustomerID int,
@Success bit OUTPUT,
@Email VarChar(55) OUTPUT,
@FirstName VarChar(55) OUTPUT,
@LastName VarChar(50) OUTPUT,
@PhoneNumber VarChar(50) OUTPUT,
@CompanyName VarChar(50) OUTPUT
AS

SET NOCOUNT ON

DECLARE @UserKey AS int

SELECT @CustomerID = CustomerID
FROM Customers
WHERE CustomerID = @CustomerID

IF @CustomerID IS NULL
BEGIN
SET @Success = 0
END
ELSE
BEGIN
SET @Success = 1
END

BEGIN

SELECT customerID, Email, FirstName, LastName, PhoneNumber, CompanyName
FROM Customers
WHERE CustomerID = @UserKey

How do I test it in management studio?

When I run a EXECUTE GetSessionInformation 56

I get this error:
Procedure 'GetSessionInformation' expects parameter '@Success', which was not supplied.

Thanks for any help!