MQTT Issue

TinyCLR OS
1

I would like to get some advice regarding MQTT.
I have one AWS IoT account and one device registered
I tested the Publish and Subscribe using MQTT Fx and it works just fine.

But can’t get it work with tinyCLR
Connection seems ok.
I can subscribe to the topic
The first time I tried to publish, I do not get any exception but data never appear in AWS.
The second attempt is done less than 2 min later. At this time, i get this exception in the console

The thread ‘’ (2) has exited with code 0 (0x0).
ConnectedChanged
Connected to MeteoDevice
Data published to MeteoData topic
Connected to AWS MQTT Broker
#### Exception System.IO.IOException - 0x00000000 (13) ####
#### Message:
#### System.Net.Security.SslStream::Write [IP: 00e4] ####
#### GHIElectronics.TinyCLR.Networking.Mqtt.MqttStream::Send [IP: 0012] ####
#### GHIElectronics.TinyCLR.Networking.Mqtt.Mqtt::Send [IP: 0008] ####
#### GHIElectronics.TinyCLR.Networking.Mqtt.Mqtt::ProcessPacketsThread [IP: 0089] ####
#### Exception System.Exception - 0x00000000 (13) ####
#### Message: Sending failed.
#### GHIElectronics.TinyCLR.Networking.Mqtt.Mqtt::Send [IP: 0026] ####
#### GHIElectronics.TinyCLR.Networking.Mqtt.Mqtt::ProcessPacketsThread [IP: 0089] ####
The thread ‘’ (13) has exited with code 0 (0x0).
ConnectedChanged
The thread ‘’ (12) has exited with code 0 (0x0).
The thread ‘’ (11) has exited with code 0 (0x0).
Data published to MeteoData topic

Code used is below.
Any advice ?

Mqtt iotClient;
var iotEndPoint = "************.iot.us-west-2.amazonaws.com";
var iotPort = 8883;
var deviceId = "MeteoDevice";

var caCertSource = Resources.GetBytes(Resources.BinaryResources.AmazonRootCA1);
var clientCertSource = Resources.GetBytes(Resources.BinaryResources._*ee1794677_certificate_pem);
var privateKeyData = Resources.GetBytes(Resources.BinaryResources._*aee1794677_private_pem);

X509Certificate CaCert = new X509Certificate(caCertSource);
X509Certificate ClientCert = new X509Certificate(clientCertSource)
{
    PrivateKey = privateKeyData
};
var clientSetting = new MqttClientSetting
{
    BrokerName = iotEndPoint,
    BrokerPort = iotPort,
    CaCertificate = CaCert,
    ClientCertificate = ClientCert,
    SslProtocol = SslProtocols.Tls12
};

iotClient = new Mqtt(clientSetting);
iotClient.PublishReceivedChanged += _iotClient_PublishReceivedChanged;
iotClient.SubscribedChanged += IotClient_SubscribedChanged;
iotClient.ConnectedChanged += _iotClient_ConnectedChanged;
iotClient.PublishedChanged += OnIotClientOnPublishedChanged;
;

var connectSetting = new MqttConnectionSetting
{
    ClientId = deviceId,
    KeepAliveTimeout = 200
};

iotClient.Connect(connectSetting);

long packetId = 1;
iotClient.Subscribe(new string[] { "MeteoData" }, new QoSLevel[] { QoSLevel.ExactlyOnce },
    (ushort)packetId++);


if (iotClient.IsConnected)
{

    var Message = "{\"timestamp\": \"2025-03-04T12:55:28Z\", \"temperature\": 21.9, \"humidity\": 37.1,\"pressure\": 101.7}";

    iotClient.Publish("MeteoData", Encoding.UTF8.GetBytes(Message), QoSLevel.MostOnce, false,
        (ushort)packetId++);
    Debug.WriteLine("Data published to MeteoData topic");

}

}

2

Tested from a WinForm app.
Works as well, so there is no config issue here

public async Task ConnectToAwsMqtt()
{
try
{
// Publish a message to AWS IoT
string msg =
“{ "timestamp": "2025-03-05T14:52:36Z", "temperature": 22.25, "temperature": 20.70, "humidity": 40.60, "lux": 359.10 }”;
var request = new PublishRequest
{
Topic = “MeteoDevice/telemetry”,
Qos = 0,
Payload = new MemoryStream(System.Text.Encoding.UTF8.GetBytes(msg))
};

     await client.PublishAsync(request);
     MessageBox.Show("Message published to AWS IoT", "Success", MessageBoxButtons.OK, MessageBoxIcon.Information);
 }
 catch (Exception ex)
 {
     MessageBox.Show($"Error: {ex.Message}", "Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
 }

}