I'm also having the same errors with S7-1200 firmware version 4.5 and azure iot hub.

I have tried the application example from siemens several times now also, 

I have tried the following:

1. Using SAS Tokens

2. Using 1883,1884,8884 ports.

3. Trying a different username based on Microsoft's documentation. {iothubhostname}/{device_id}/?api-version=2021-04-12

Still azure keeps rejecting me with 80C5 status code.

Azure shows some messages were used --> does this mean the rejection message to the S7's connect request?

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Split from S7-1200/-1500 MQTT to Azure IOT-Hub .