I finally got mine to work. I installed this switch in my garage where my old switch was only connected to a black (load) wire, a red wire, and a copper wire. Behind the switch was a pair of white wires which were wirenutted together and not attached to the old switch. This was the only wall switch that controlled this particular light (garage ceiling light installed by my builder then the home was build in 2004).

After removing the old switch, I connected the black wire from the wall to one of the two black wires in this new switch. I connected the red wire from the wall to the other black wire in the new switch. I connected the two white wires I found in the wall (which were connected to themselves but not connected to the old switch) to the white wire in the new switch. And, I connected the copper wire from the wall to the green wire in the new switch.  Works like a charm.  Photo attached below.

I hope this helps others who may have the same problem and stumble onto this discussion.

  @Engineer_Dan 

I have the same issue. My light worked fine for 16 months and now it stopped turning on the light. The HS200 switch is wired correctly (it worked flawlessly for 8 months). I have 10 of these switches installed and this one just stopped working. It responds when turned on/off using the app and Alexa but the actual lights do not come on.

I've done the following troubleshooting:

• Wiring is correct. It worked great for 16 months. LOL
• I've changed the bulbs and they lights still do not come on.
• The old bulbs work fine in other fixtures.
• I put the old switch back on the circuit and it turns the lights on/off.
• I reset the HS200 switch and I still have the same issue.
• The switch does come on (not the fixture lights) using the app or manually pressing the button.

Seems like the switch has just died after 16 months. Any other suggestions? 

It is a little disappointing that TP-Link has not responded to these posts. 

  @Arlix You are a genius!!! After many frustrating hours, this totally worked. Thanks!

Arlix wrote

@Engineer_Dan Problem solved! Initially, I had exactly the same issue: the switch is fine but the lights don't turn on. Then I realized that the whole bundle of neutral wires need to be link to the switch. I figured that out when I came across a wiring map from another company. I was misled by the instruction that I connected only one neutral wire to the switch, and that was the mistake. Hope that helps.

  @Osugrad  Spectacular! That was exactly my issue. You set me on the right path. Picture helped immensely. Thank you!

  @Arlix Another +1 for this! Using both neutral wires that were in the box instead of just one solved the problem for us! THANK YOU!