I have IOT devices (Pi Zeros) listening to an MQTT broker to control power sockets around the house. IFTT is used to create custom Google Assistant voice commands:
"Hey Google, lights on" -> Google Nest Mini -> IFTTT -> MQTT Service -> Raspberry Pi -> Energenie Smart Socket
I had been using an http tunnel to expose the Pi to the web but decided, when I bought a second Pi, to move to a more appropriate solution.
The data itself is simple JSON payloads. I got it working pushing events to the broker manually but the authentication issue meant I couldn't use IFTTT with Flespi.