@nicholus.h how do you know it current senses? 

@Chicago_SH I did install one smart 3 way switch over the 4 way circit and everything works fine just as a normal 3 way switch replacement

@septer012 Can I substitue the HS220 for the HS210

@Donley no the dimmer is not a three-way. 

@Chicago_SH appreciate this thread. I didn't realize I had a four way wiring set up when I bought the product. I am definitely not an electrician so this diagram saved me an hour and a trip to the hardware store to return the product. I am sure of it. Thank you. 

@septer012 

I had an electrician install two Kasa 3-way switches at each end of my 4-way set up, leaving the middle switch a dumb switch (the one with 4 wires). It never did work, even using the Kasa installation option on the app for having 2 switches for one light set. The one thing I wonder about is that these two Kasa switches came from different boxes. Does that matter?

I had previously purchased two Kasa 3-way (HS210) switches and installed one switch from each into different 3-ways. (To be clear, I had two 3-way set-ups and each got one smart switch.) So I had a left-over switch from each box. Those are what I installed into my 4-way, which never worked. Does that matter? Are the two 3-way switches that come in one HS210 box somewhat linked?

@SWHighlander 

Not sure, mine work, and some others here.  I can only suggest to make sure you program in the APP the line in side first then the load side second in case that matters. 

@Chicago_SH This is great information, thank you! Is it possible to add a dimmer to this mix?