@LAWoman9 

If neither the physical switch or the app is not doing anything, something may have failed in the switch.

You could try double-checking the wiring, but if that looks normal I would reach out to our support at that point.

@Tony Thanks for the reply. I have reached out to customer support, but they keep asking me to try different things - which means I have to get someone over every time to look into it. I'm 95% sure there is something wrong with the switch and it's still under warranty. It is really annoying to have to jump through all these hoops to get a replacement. It's not like a smart plug - this is hard wired in the wall. :( 

@LAWoman9 

The same thing happened to me. Proving to TP-Link the switch was defective was a real ordeal. Adding insult to injury, they require you to ship the defective unit back at your expense. I have to assume this must happen with some regularity and they try to disincentivize the customer from pursuing warranty claims. As a result, I will avoid the brand in the future.

@Tony 

I Have recently had the same issue with 2 of the 13 dimmers I've installed. Light stays on and will not respond to the switch or the app. (Although both show the state toggling from on to off. 
 

cycling power at the circuit breaker has resolved the issue twice, but I am concerned it will recur.