Control HA Services from Another HA Device

I am in the middle of moving from a single dedicated HA RPi to moving all of my automations off to a new RPi 3B+ I have all the state changes coming through mqtt statestream, so I can use these for triggers of my automations. I now need a way to turn services on and off on the remote HA instance, I want to be able to sound the alarm on my Xiaomi Gateway or turn on boolean’s for example. Is there a way of doing this?

You could call the other instance via REST API:

Thanks I decided to go full blown node-RED and have to say can’t believe I waited this long to bring all automations across.