Don't push down when you try it flick your heel straight out like you do with a heelflip

What i do is the ninja kick

Back foot position - on the center of tail Front foot position - your big finger stay off the board. Now flick the heelflip more sharper, This should be a sharp move, that's you do your rib of foot.

Keep your foot in the centre of the board and just try, it takes a long time to see how to flip it

The important thing you had to do is to flick diagonally between the tail and the center of your board (sorry for my bad english I’m french 😅)

Try to find other feet position, i usually do it with both feet in paralel