Azure IoT Hub, push from device fails every time with connection closed, even using mosquitto_pub

Question

I have a free Azure Iot Subscription and I created a Hub with few devices. I have a embedded device that connects with MQTT DIRECT to Azure IoT Hub using SAS method.
https://learn.microsoft.com/en-us/azure/iot-hub/iot-hub-mqtt-support#using-the-mqtt-protocol-directly Basic connection is OK (otherwise I get connection refused)
But PUSH always fails and Azure closes connection and I cannot see any messages in Azure Iot Explorer Telemetry. Subscribe is OK also, I can subscribe from embedded and receive messages, including from Explorer when I use C2D Messages. I said to try with another client.
Thanks to this post, I configured mosquitto_pub for test purposes (sending messages)
Connecting Mosquitto to the new Azure MQTT backend

.\mosquitto_pub.exe -h XXXXX.azure-devices.net -u "XXXXX.azure-devices.net/mydevice6" -P "SharedAccessSignature sr=XXXXX.azure-devices.net%2Fdevices%2Fmydevice6&sig=WA9qbn7Xa%2FQ%2F90CL7PgnNoD8AllWW757QvGJ3s2Ik2E%3D&se=1681536409" -t "devices/mydevice6/messsages/events/" -p 8883 -d -i mydevice6 -d -V mqttv311 -q 1 -m "{""key"": ""value""}" --cafile "DigiCertGlobalRootG2.crt.pem"
Client mydevice6 sending CONNECT
Client mydevice6 received CONNACK (0)
Client mydevice6 sending PUBLISH (d0, q1, r0, m1, 'devices/mydevice6/messsages/events/', ... (12 bytes))
Error: The connection was lost.

Again, appears that mosquitto_pub works just fine, if I change device ID, signature, or others stuff, I immediately receive "Connection refused" The behavior is exactly what I see on my embedded device, I receive ACK from server, appears that I am able to PUSH, but push where??? The connection shall remain online, instead, Azure it closes immediately. I think this is some kind of stupid mistake, or some bad Azure configuration. I did another test, this time, successfully, from C# (using SDL examples)
I created a small console app, with these parameters

static DeviceClient deviceClient;
static string deviceConnectionString = "HostName=XXXXXX.azure-devices.net;DeviceId=mydevice2;SharedAccessKey=xP+WyHL1quc4ax9pQ7Fc8oKuhs/0iC5dSKH2yUqIjzM=";

            MyData data = new MyData { Id = "Param", Name = "Value" };
            var serializeData = JsonConvert.SerializeObject(data);
            var commandMessage = new Message(Encoding.ASCII.GetBytes(serializeData));

            Console.ForegroundColor = ConsoleColor.Blue;
            Console.WriteLine("Send Message: {0}", serializeData);
            Console.ResetColor();
            Console.WriteLine("");

            await deviceClient.SendEventAsync(commandMessage);

This time message can be seen in Azure IoT Explorer. Now why my embedded device and mosquitto_pub appears that PUSH messages, but

• I cannot see them anywhere
• Azure immediately disconnects

I am stuck from few days by now, everything I do, I can connect, Azure sends ACK, but PUSH messages are simply replied with "connection lost". Any help greatly appreciated!!!

Answer 1

Hello,

It looks like there might be a typo in the topic name you're using in the mosquitto_pub command.

The correct topic for sending device-to-cloud messages should be devices/{device_id}/messages/events/.

In your case, it appears to be misspelled as devices/mydevice6/messsages/events/. The extra 's' in "messsages" is causing the issue.