How could i perform a check on when ever a publisher publishes something about umqttbroker HOT 3 OPEN

The demo example does that already.
Try to connect from a remote client and publish something - **the console will show this as well**.
Look at data_callback.

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yes i can see the data at the console but i want to trigger some gpio high when ever a specific topic is published

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Do a subscription on the specific topic with "MQTT_local_subscribe((unsigned char *)"yourtopic", 0);" and in the "data_callback" check the topic and the data and trigger the gpio.

You might also consider to use my https://github.com/martin-ger/esp_mqtt project, there you can do this with an even simpler script.

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