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Within a customer subscription, we're running into an issue related to C2D messaging where messages sent to devices connected via the MQTT protocol are sometimes rejected.
The general setup is that all devices (PLCs) are connected to an IoT-Hub via MQTT.
Each device may receive inputs from a related service which uses the ServiceClient class in the Microsoft.Azure.Devices package to send C2D messages.
The IoT-Hub itself is accessed only through a private endpoint and public access is blocked.
Sometimes, the IoT-Hub metrics display rejected messages. However, this shouldn't be possible according to the relevant documentation. It states:
Devices that connect over the Message Queuing Telemetry Transport (MQTT) Protocol can't reject cloud-to-device messages.
There are no devices connected that use a different protocol.
Are there other possible reasons a C2D message may be rejected?
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Hello @Darius Kinstler Welcome to Microsoft Q&A Platform and thanks for your query.
Could you please add more info to the question, such as the Azure IoTHub metrics showing the 'Rejected Messages'?
Any logs which can add more clarity to the scenario?
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@Darius Kinstler I am running in to this exact same issue. It seems the ServiceClient.SendAsync method uses AMQP to send the message (at least, according to the documentation). Devices that connect via AMQP CAN reject messages. The part of this that troubles me is that my device does not mention it supports AMQP, only MQTT and HTTPS. I have yet to figure out how to require the message gets sent with MQTT. Maybe @QuantumCache knows how?
Hello @Tim_Myth Sorry for the delayed response.
This thread discussion was very old, and somehow i missed the alert, so sorry for that .
Could you please create a new thread if you still looking for any further assistance? we are happy to help you further.
we will close this thread and please create a new thread so that we can help you better.
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If I use MQTT protocol and .NET SDK v2 on device side, my c2d messages are rejected. I described this issue here - https://github.com/MicrosoftDocs/azure-docs/issues/98930#issuecomment-1596319291
Hello Team, Please make use of the latest documentation on the Azure IoT Support for MQTT protocol.
Communicate with your IoT hub using the MQTT protocol
IoT Hub MQTT 5 support overview (preview)
Please comment in the below section and we would be happy to help you further in this matter.