After Effects 2025.1.0 - can't figure out how to trigger animated typewriter effect with audio

I have a project set up where I'm trying to type out the words "THIS IS A TEST" and have each character appear on screen the moment the typing sound occurs:

So after following a lot of youtube tutorials, here's what I did:

[1] Took the audio file and converted it to keyframes and noted the amplitude of the typing sound being around 2.0 units

[2] Applied "Opacity" animator to Text layer, switched Units from "Percentage" to "Index", set Smoothness to "0", and set Range (not Layer) Opacity to 0%.

[3] Pickwhipped Range Selector Start to Audio Amplitude Slider. 

I'm not getting the desired result: typewriter text is not animating to typing sound. I'm sure I'm doing sometihng wrong, but I have no idea what.

Thank you so much to anyone who can help me resolve this.