This is a common issue as it is worded a tad weirdly. To do this, do not simply do a double back/frontflip then a 720 (or vice versa) as a 360/720 back/frontflip is different. To do this move, spin diagonally in the air. It may take a few tries but you should get it eventually. Hope this helps! (I also recommend using the paraglider to slow your fall)