How do you implement blend tree animation aiming in a third-person shooter?

Hello. I have created multiple gun aiming animations that I would like to interpolate between by moving the mouse up and down. I have set up a blend tree with the animations, with thresholds of -90, -45, 0, 45, and 90, just like in a video I saw by Royal Skies LLC, but I’m having trouble with the coding part. I tried, “animator.SetFloat(“aim”, Input.GetAxis(“Vertical”));” but the float doesn’t seem to be changing when I move the mouse, and thus the animations aren’t playing.

Here is the video for anyone who might be interested: (from 1:09 onward is the part that I followed) Unity 3D Animation Masks & Avatars (3rdPS/FPS Aiming In 2 Minutes!!!) - YouTube

So, apparently, “Vertical” is for a gamepad, and “Mouse Y” is what I needed for the mouse. Now, however, the character is snapping back and forth between the desired pose and its forward aim pose while I’m moving the mouse around. How do I get the desired pose to stick?