There's a step in the installation instructions in the app that says "connect the neutral wire using the provided wire nut". However in the picture displayed the wires are highlighted in green, and I assumed the green wire coming out of the back of the unit is the neutral wire (which it is not) and connected the green wire to the neutral wires in the wall.

This causes the kasa smart switch to flicker on and off and turns the light on and off repeatedly. I quickly turned off the circuit breaker and retraced my steps to see where I screwed up and caught my mistake. I had to remove the green wire from the neutral wire nut and replace it with the white one which then made it all work.

Anyway, thought I'd share in case someone else makes this mistake or maybe someone that works on the app can add a note to that screen that the neutral wire is white, not green. Feels dumb because it's labeled on the unit, but the image in the app tripped me up a first time installer...