[Python] Azure Function (python) won't trigger from Azure IoT Hub event

I have an IoT Hub and an Azure Function App written in Python. I want the Azure function to trigger on messages received by the hub.

The IoT Hub is publicly accessible and I can successfully send messages to it. I have confirmed the JSON payloads are being received by using the Azure CLI.

I've deployed the Azure function using VS Code (Azure extension) and the function.json looks like this:

{
"scriptFile": "__init__.py",
"bindings": [
{
"type": "iotHubTrigger",
"name": "event",
"direction": "in",
"eventHubName": "iothub-ehub-[redacted]-36471244-3e33dca112",
"connection": "IoTHubConnectionString",
"cardinality": "one",
"consumerGroup": "mydevices"
}
]
}


My python function (in __init__.py) starts with:

def main(event: func.IoTHubEvent) -> None:
...


In the Function App on the Azure Portal I have gone to Settings > Environmental Variables and set IoTHubConnectionString to Endpoint=sb://ihsuprodlnres017dednamespace.servicebus.windows.net/;SharedAccessKeyName=iothubowner;SharedAccessKey=[redacted];EntityPath=iothub-ehub-[redacted]-36471244-3e33dca112

I've been struggling for a while now and I can't get the function to trigger, the Function App logs show nothing so I have no idea what's wrong.

How can I troubleshoot this?

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