Question on

What is the difference between client and player?

Here’s how I think of the term player is the human pilot in a single player mode and client is the proper term for the human slot in a multiplayer mission. Is that correct I do ot recall the options being described in the user manual but I may have missed it?

There can only be one player aircraft in the mission. If you have 1 or more client aircraft then when you start the mission you will get a prompt showing a team and then aircraft selection. When its just a single player aircraft you spawn directly into the aircraft.

Also failures and cockpit related triggers only work on player aircraft.

"Client" aircraft slots are offered at the beginning of the mission as choices. If a slot is not chosen by a pilot, the plane does not spawn. "Player" slots are filled by the pilot when the mission is started. Generally speaking, client slots are used to offer choices to players in multiplayer missions, and player slots are for single player, single aircraft missions. The distinction is not set in concrete. The single player missions I build for myself use "client" slots because I want the single player to have a choice of aircraft to fly. I've never tried, but I don't think you can mix the two in a mission.