It won’t work with a momentary switch because by definition a momentary switch immediately turns on and then off.
Instead, you need to use a binary switch like the “simulated switch” device type. This is detailed in the Harmony/Alexa FAQ.
Alternatively, you can use a momentary switch, but then you have to say something like “Alexa, turn on Exit Routine,” where “exit routine” is the name of the momentary switch and it is the switch coming on that triggers the power off activity.
A binary switch is like a traditional light switch toggle. It has two states, on or off. When you turn it on and it stays on until you turn off again.
In contrast, a momentary switch is like a traditional doorbell button. It is off most of the time, and activation causes it to come on for just a moment and then return itself to the off. This is why it doesn’t really make sense to turn off a momentary switch. It is already off.
You will find additional detail discussion of how to synchronize off in the harmony/IFT TT project report, even though you will probably not be using IFT TT is a middleman, but instead will use the harmony trigger smartapp. The switch configuration and power off protocols are the same though.
