LoRa Heltec V2 doesn't send ACK to the downlink messages

Hi there,
I’m using the ESP32_LoRaWAN-master library in the class “C” mode. I’m sending downlink packets, the node receive them, it doesn’t respond with the confirmation to the gateway.
I believe that some configuration has to be enabled, but I can’t find it.

Thanks in advance.
Best regards


could you show more details?