I bought round-trip tickets for winter holidays to Sofia, Bulgaria from Moscow, Russia with a 14-hour connection in Amsterdam, Netherlands. I want to buy an extra piece of luggage in order to take my ski equipment.
The problem is that each of the 4 flights (Moscow-Amsterdam, Amsterdam-Sofia , Sofia-Amsterdam, Amsterdam-Moscow) is with different airlines (Aeroflot, Bulgaria Air, Transavia, KLM respectively). However all tickets were bought from KLM. Due to these facts I'm confused how many times I should pay for an additional piece of baggage and should the payment be made to KLM or to any company at the airport?