Send amqp message with headers in quarkus

I want to send a Java (well Kotlin) POJO as JSON in an AMQP message to RabbitMQ using Quarkus.

@Path("/amqp")
class TestSource {

    @Inject
    @Channel("amqpwrite")
    lateinit var emitter: Emitter<MonitoringStatusDto>

    @POST
    @Path("/send")
    fun sendMsg() {
        val status = MonitoringStatusDto(status = "OK", message = "test amqp write")
        emitter.send(status)
    }
}

On the rabbit queue the message is received as base64 encoded byte stream.

How can I set the headers here to put the content type in it? Also header settings like TTL might be interesting.