Read payload as string

Source/ProofOfConcept/Services/MQTTClient.cs

@@ -1,3 +1,4 @@
+using System.Text;
 using Microsoft.Extensions.Options;
 using MQTTnet;
 
@@ -21,8 +22,9 @@ public class MQTTClient : IHostedService
         
         this.client.ApplicationMessageReceivedAsync += (e) =>
         {
-            logger.LogInformation("Message received: {Message}", e.ApplicationMessage.Payload);
-            messageProcessor.ProcessMessage(e.ApplicationMessage.Payload.ToString());
+            string message = Encoding.UTF8.GetString(e.ApplicationMessage.Payload);
+            logger.LogInformation("Message received: {Message}", message);
+            messageProcessor.ProcessMessage(message);
             return Task.CompletedTask;
         };
     }