Mqtt downlink ACK

I’m new to chirpstack. I have two questions:
1/ What’s the “reference” field used for in downlink frames?
2/ For mqtt integration, and for a confirmed downlink, how can we know which aknowledgment corresponds to which downlink frame ? ( The FCnt is not sent back after queueing a downlink using mqtt publish)
Thanks in advance, @brocaar

@brocaar To be more precise: is FCnt returned back along with the reference when shceduling over MQTT ?

Using the MQTT enqueue, you do not get back the fCnt. In this case it is better to use the API, in which case the response is the fCnt or in ChirpStack v4 the ID of the downlink.

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