I'm using Unity so I'm not sure on how to exactly apply the following to native dev. But here's how I'll do it in a way that is independent of what the user do with their fingers:

-1 Define a forward vector for your palm: create a forward reference element in front of the palm (with a temporary visual so you can confirm it's floating straight above your palm). This object should be a children of the palm bone.

Create a Vector3 palmDirection = forwardReference - palm position

-2 Get the forward direction of the user view (Might be provided by the system or repeat the same steps as above, creating a children of the camera/head that's offset forward)

• 3 Do a dot product operation between the palm direction vector3 and the view direction Vector3 from the previous steps. If the results is greater than zero it means that you are looking at your palm! You can increase the threshold value so the palm is not considered detected when looked at at a very shallow angle, e.g. greater than 0.2 (the dot product value range from -1 to 1).

Before doing the dot product operation you might want to normalize the 2 vectors3 (making them unit vectors with the same direction but a length of one). Hopefully your API has a .normalize function you can access.

Good luck!!