I have been installing smart switches in my house for the most common lights and I needed a 3-way switch. I have been using all TP-Link Kasa switches so I bought their 3-way switch on Amazon for around $67. A few reviews said you really only needed one Kasa switch as long as the other was also 3-way. This worked for me and left the other one for use elsewhere. I decided to use the other switch for a single pole use, but I needed to figure out the wiring. I know next to nothing about electrical wiring so I got it wrong on the first try. I then discovered the proper wiring, at least for my house, was as follows:
- Neutral to neutral (white wire from house to white from switch)
- Ground to ground (bare wire from wall to green from switch)
- Powered wire to line/load (common) wire (black wire from wall)
- Powered wire to traveler (red wire from wall)
- Other traveler left open/unused
Misdirected Request 
I also tried to use a solitary HS210 in a single-pole application but could never get it to work. Upon contacting TP-Link support, they told me it wasn’t possible.
In your original single pole switch (the one you replaced), was the red wire connected to your light (the load) and the black was hot, or the other way ’round?
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