Convert UI element screen position to world position

I want to instantiate a GameObject at the screen position of a UI button, which is on a Screen Space - Overlay canvas. My current code is:

 Vector3 buttonWorldPosition = localCamera.ScreenToWorldPoint(inventoryButton.transform.position);

However this does not seem to work as desired because the UI button's transform.position is (-30, -30, 0), despite it being positioned in the top right of the screen.

Any ideas?