Client using Kotlin

I’ve successfully connected and sent mqtt messages to mosquitto broker and using current Kotlin on Android Studio. Since I’m pretty new to andriod programming i got stuck in the subscribe callback part of the mqtt client and can’t find any examples that could boost my knowledge.
// Setup MQTT Client
val client: Mqtt3BlockingClient = Mqtt3Client.builder()

// Connect with MQTT Client
try {
val connAckMessage = client.connectWith()
Toast.makeText(applicationContext, connAckMessage.toString(), Toast.LENGTH_LONG).show()
} catch (e: Exception) {
Toast.makeText(applicationContext, “Kotlin Fehler beim Senden”, Toast.LENGTH_LONG)
} catch (e: java.lang.Exception) {
Toast.makeText(applicationContext, “Java Fehler beim Senden”, Toast.LENGTH_LONG).show()

var counter:int = 16


All works fine up to here.

But i can’t really find out how to implement the callback.

works fine, gets compiled and gives the expected results. I’m just stuck on how to get hold of the subscibed Payload instead of just printing it to debug output…

any help that points me into the right direction would be appreciated!