Since the altitude value for a waypoint is relative to takeoff height. Is it possible to get the drone to go to a negative altitude relative to the takeoff height in a waypoint mission?

The use case would be a pilot taking off from a height above the mission. For example a user is 45m above on a hillside and wants to fly a mission that is 15m above the ground in the valley. So the drone needs to go -30m downwards (once it has cleared the slope). I've tried to do this in the simulator but the drone will only go to 2m above take off distance. I also tried the same using virtual sticks but the drone would only go down to 1m. I'm unsure if this is a limitation of the simulator or if the simulator needs some extra information such as the elevation at a coordinate or if this can even be done when flying for real

Set the altitude property for the DJIWaypoint to -30.
DJIWaypoint * second_waypoint = [[DJIWaypoint alloc]init];
CLLocationCoordinate2D point_coordinate = CLLocationCoordinate2DMake(your latitude,your longitude);

second_waypoint.altitude = -30;
second_waypoint.coordinate = point_coordinate;
Should work under real conditions.

Yes. The minimum altitude of the waypoint is -200m