Request the data of energy meter in Home Assistant(modbus/tcp), trigger the Sonoff in realtime.

Описание

https://www.iammeter.com/newsshow/blog0718-modbus-tcp-sensor-controrl-home-assistant-relay

How do find the power meter with regard to your requirements
https://www.iammeter.com/newsshow/blog-find-power-meter

The Wi-Fi energy meter
single phase energy meter:https://www.iammeter.com/products/single-phase-meter
and
three-phase energy meter https://www.iammeter.com/products/three-phase-meter
support Modbus/TCP, like this
https://www.iammeter.com/newsshow/news-modbus-tcp-energy-meter

So you can request the data into Home assistant by modbus/tcp sensor.

The most advantage of Modbus/tcp sensor in Home Assistant is it supports requesting the data every 1 second, which can be used as a real-time sensor feedback value in a control loop. The 1-second sample interval makes it can be used in many interested things

Four ways to integrate the Electricity Usage Monitor (IAMMETER) into the home assistant:
https://community.home-assistant.io/t/four-ways-to-integrate-the-electricity-usage-monitor-iammeter-into-the-home-assistant/485520

Beginner tutorial: how to use a Wi-Fi energy meter in the home assistant:https://imeter.club/topic/392

How do find the power meter:https://www.iammeter.com/newsshow/blog-find-power-meter