Lua relative waypoint

Hi I’m working on a script that is meant to set landing plan so if I enter rtl the drone lands with my waypoints. I’m having trouble with setting waypoints’ altitude because when the code sets them it’s always absolute altitude and when I set them they are relative. I have searched through documentation and I haven’t even once seen a place in mavlink_mission_item_int_t() to distinguish between absolute and relative altitude.
any help would be welcome