When you work with Paho MQTT v2.0.0 or later versions, you might encounter an "Unsupported callback" error. This error occurs because v2.0.0 introduced breaking changes, meaning code written for v1.x will not function properly without modifications.
To resolve this issue, you can either add a parameter to specify the callback API version or install an earlier version of the library.
Adding a Parameter
In your code, locate the line where you create the MQTT client:
client = mqtt_client.Client(client_id)
To specify the callback API version, add the following parameter to the Client() function:
mqtt_client.CallbackAPIVersion.VERSION1
Your code should now look like this:
client = mqtt_client.Client(mqtt_client.CallbackAPIVersion.VERSION1, client_id)
This change will configure the library to use the v1 callback API, making it compatible with older versions of the library.
Installing an Earlier Version of the Library
If you prefer, you can also install an earlier version of the Paho MQTT library (v1.6.1 or earlier). To do this, run the following command:
pip install paho-mqtt<2.0.0
This command will install the latest version of the library prior to v2.0.0, which will not have the "Unsupported callback" error.