From Onset Developer Wiki
This event is called when a player enters a vehicle.
OnPlayerEnterVehicle(player, vehicle, seat)
The player is entering a vehicle.
The vehicle in which he is getting in.
The seat of the vehicle.
AddEvent("OnPlayerEnterVehicle", function(playerid, vehicle, seat) if seat ~= 0 then AddPlayerChat(playerid, "You have entered the vehicle "..vehicle.." as a passenger.") end end)