IoT C2D Messages from Dynamics 365 Business Central

IoT C2D Messages from Dynamics 365 Business Central

My example invoke an Azure IoT Hub Device Method from Microsoft Dynamics 365 Business Central.

Happy New Year

Required information to send a message to from IoT Hub to the IoT Device endpoint are:

A device method will be invoked by calling the method on the Device Twin by using this Url:


(API Documentation – Invoke Device Method)

The message content is Json. Key methodName specify the called method and payload contains the data (parameters) for the method call:

    "methodName": "<Methode-Name>",
    "responseTimeoutInSeconds": 200,
    "payload": {
        "<Param-1>": "...",
        "<Param-2>": 0,
        // ...

IoT Hub SaS Token

The IoT Hub SaS token can be created by using the Azure IoT Hub Toolkit VSCode Extension.

IoTHub-SaS Token

Select your IoT Hub and generate the SaS Token for the IoT Hub. 


IoTHub-SaS Token

Business Central

The user interface is a CardpPage with some fields to enter the needed information. Finally an action Send C2D Message will send the message to the specified IoT device.

Happy New Year

In the example, C2D messaging is done by a HTTP POST call to the IoT Hub. And HttpClient in Microsoft AL is your friend!

These lines of code from the Action Trigger shows, how-to prepare the HttpClient, add the message content and send the message to the IoT Hub:

    content: HttpContent;
    client: HttpClient;
    response: HttpResponseMessage;
    uri: Text;
    json: text;
    // Prepare the URL
    uri := StrSubstNo('%1/twins/%2/methods?api-version=2018-06-30', mHubUri, mDeviceId);
    // Add the Authorization Header:
    // 'SharedAccessSignature'
    client.DefaultRequestHeaders().Add('Authorization', mAuthorizationToken);

    // Add the message Json
    content.WriteFrom(StrSubstNo('{"methodName":"%1","responseTimeoutInSeconds":200,"payload":{"message":"%2"}}', mMethod, mMessage));

    // Call the IoT Hub
    client.Post(uri, content, response);

    // ...

The result HttpResponseMessage from the call is presented in a FactBox of this page.

{"status":200,"payload":"Happy New Year from Device!"}

WeMos D1 mini with Arduino

The device is an ESP8266 WeMos D1 mini shield combined with sensor for soil moisture measure ment and an OLED shield.

WeMos D1 mini

My used sketch is based on the IoT Hub Feather HUZZAH Client application example. To show the incoming message from BC, I modified the file iothubClient.ino and added a method to display the message, wrapped in the payload:

const char* showMessage(const unsigned char* payload)
    // Display the Message in OLED
    // ...

    return "\"Happy New Year from Device!\"";

int deviceMethodCallback(
    const char *methodName,
    const unsigned char *payload,
    size_t size,
    unsigned char **response,
    size_t *response_size,
    void *userContextCallback)
    Serial.printf("Try to invoke method %s.\r\n", methodName);
    const char *responseMessage = onSuccess;
    int result = 200;

    if (strcmp(methodName, "showMessage") == 0)
        // ** Handle the incoming message from Business Central **
        responseMessage = showMessage(payload)
        Serial.printf("No method %s found.\r\n", methodName);
        responseMessage = notFound;
        result = 404;

    *response_size = strlen(responseMessage);
    *response = (unsigned char *)malloc(*response_size);
    strncpy((char *)(*response), responseMessage, *response_size);

    return result;

The received message from BC at the device is:

    "methodName": "showMessage",
    "responseTimeoutInSeconds": 200,
    "payload": {
        "message":"Happy New Year MSDyn365BC"

Related Information (C2D Messageing)

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