When you are trying to add travelers to an itinerary, please follow these steps:
Step 1: select the itinerary or itineraries you are booking
Step 2: you will be redirected to the trip summary page. You can change the number of passengers by clicking on the "Add traveler section" (this is located on the top right-hand corner).
Please, make sure that all travelers that are being added to your itinerary have government issued photo ID on the day of the trip.