To include a link upon booking, you'll want to enter the link under How To Access. To do this, first login to your Partner Dashboard. Then select Listings and locate the activity you want to add the link for. Once you select the activity, click on About. You'll see the How To Access field and can enter the link there. Note that this will only show after a member makes a booking.
Hope this helps! If you have any other questions, please let us know at firstname.lastname@example.org