The day of your activity, you just have to show your booking ID to the provider of your activity. You can find the booking ID in your confirmation email. It is a 6-digits code (letters and numbers): Eg. CHYET1.
*NOTE: The booking ID is not the order number (P-XXXXXXXXX). The order number is only for you, the provider of the activity will have your slots booked under your booking ID and customer name.