Purchase add-ons even after buying a ticket or even the ticket was booked via online/travel agency. Baggage fee at the airport is more expensive.
Online check-in is a free service. Available on all scheduled flights. Online check-in opens 30 days before the scheduled departure time and closes 40 minutes before the scheduled departure time on domestic flights within Kazakhstan and 60 minutes on international flights. The categories of passengers who can check-in online are listed here