You can record and keep track of traveller deposits and payments due on the Payments tab of each itinerary (Incoming Payments).
You can create individual records by selecting the 'Create incoming payment'. Alternatively, you can select the option to 'Apply [a] payment schedule' which will automatically generate multiple payment records e.g. deposit, 2nd payment & final installment. You can create and tailor payment schedules in your Organisation settings (Organisation > Defaults > Payment schedules).
You can also display a Payment Timelines on an itinerary so travellers can keep track and see when payments are due. This can be enabled by ticking the 'Show payments timeline on the itinerary' check-box in the bottom left-hand corner.