Wait for the board to rise before flicking
Mechanism / Why It Happens
Flicking too early causes the board or nose to slam into the ground
In a kickflip, rotation is generated by flicking through the side of the nose after the board has reached a sufficient angle. On the other hand, if you apply force to the nose while the board is still flat, even if it starts to rotate, you end up pushing the entire board downward, causing it to slam into the ground. To fix this issue, practicing only the front foot motion can be effective. For more details, see this Tip (Link).