The position of your chest is usually important. If it’s too far over your toe side on heelflips the board will land behind you. The kick should be sudden and not too early.
Before learning flips, it might help to learn shove-its (including 360 shove-its) if you haven’t already as they involve a jump, a strike of the tail and a catch as well.
On simple pop shove-its you can get away with a sort of aggressive kick turn and a jump to begin with, but rotating the board off the back wheels like that on a 360 shove-it will cause the board to travel out from under you as it spins. The solution is to throw your weight earlier and sweep the wheels off the ground and round behind you so the board spins round its middle. If the board does half a pressure flip as it spins, try keeping the heel of your back foot down as you strike the tail.