For now, this is the best Harmony Hub integration solution that I have found. It has been incredibly reliable. Just don't remove your SmartThings-Harmony integration, as the keys from that one are 'borrowed' by this one. They need to stay valid!
I created a simple Device Driver to work with the Google Home Assistant Relay nodejs server running on a Raspberry Pi. It uses 'Broadcast" messages to all of your Google Home devices.
And I wrote the original Pushover Driver for Hubitat, which has now been added to the Hubitat Firmware as a native integration. Here's some useful information about setting it up. No need to use the driver from this thread. Just use the built-in one.
