Azure IoT Hub never receives the message

This tutorial code a simulated IoT device app that sends device-to-cloud messages using Azure IoT Hub. This app works as advertised. I am able to see the telemetry data in Azure.

This companion tutorial builds an app to send messages to the simulated IoT device app in the first tutorial (presumably) over MQTT. The first thing they have you do to enable this is add the following code:

var client = DeviceClient.fromConnectionString(connectionString, Mqtt);  
  
client.on('message', function (msg) {  
  console.log('Id: ' + msg.messageId + ' Body: ' + msg.data);  
  client.complete(msg, function (err) {  
    if (err) {  
      console.error('complete error: ' + err.toString());  
    } else {  
      console.log('complete sent');  
    }  
  });  
});  

Note the specification of Mqtt parameter in the fromConnectionString call. The second app uses ServiceClient.SendAsync to send the message. It uses the following code to send a message:

private async static Task SendCloudToDeviceMessageAsync()  
{  
     var commandMessage = new  
      Message(Encoding.ASCII.GetBytes("Cloud to device message."));  
     await serviceClient.SendAsync(targetDevice, commandMessage);  
}  

As is, the simulated IoT device never receives the message from the C# app. The ServiceClient.SendAsync Method documents that it is sent over AMQP. As noted, the first app clearly uses Mqtt.

I question whether the AMQP protocol is the issue. Can anyone point me in the right direction to troubleshoot where the message goes and why the app never receives it?