How can I wire this light switch that expects three wires but I have only
two coming from my circular flourescent ceiling light?

I bought the Legrand "WattStopper RS-150BA-N Vacancy Sensor Switch with
Nightlight and Manual on/off" whose specifications say it's for a "single
pole circuit", 120V/60hz, 1/6HP fan, 0-600 watt incandescent or flourescent
light.

The switch has four (4) wires labelled
1. black = hot
2. white = neutral
3. red = load
4. green = ground

The instructions say
a. Connect the green wire on the switch to bare wire ground (if any)
b. Connect the white wire on the switch to the "neutral wire"
c. Connect the black wire on the switch to the "power wire"
d. Connect the red wire on the switch to the "load"

The problem is the box in the wall has only two wires.
1. black
2. white

The ground is optional so what I'm confused about is how to connect the
white wire from the circuit. Do I connect it to the red wire or the white
wire on the switch? There are no other wires in the brown plastic box.

I keep calling the technical support number 888-817-0571 but it always says
it's temporarily unavailable.

Can you advise me how to wire black/white/red on the switch to black/white
in the wall?