Downlink data (confirmed and unconfirmed) doesn´t work

I have a sensor device connected to my ChirpStack and I want to send downlink data to that device. So I fill out the Enqueue downlink payload area

and schedule the downlink.

My device is sending some uplink data and they appear in the LORAWAN FRAMES´ window but as UnconfirmedDataDown`.

Also, the LoRa module (RAK3172) doesn´t output received data. Why does ChirpStack output UnconfirmedDataDown when I have selected confirmed data? Do I have to change something in the configuration to use downlink in confirmed mode?

Figured out the problem in the documentation: Note: After a device (re)activation the device-queue is flushed.
I have started every transmission during the join cycle by using the web application and this discards the queue.