Issue on AWS IoT Core downlink with TTN via MQTT

Application Development AWS
1

I had set up TTN working with AWS IoT Core. I could subscribe uplink topic without problem but got issue on downlink. How to debug this? The proper encode function was implemented and verified locally.

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2

I tried to use Python program to access MQTT of TTN. Uplink is working but downlink is still failure.

handler = ttn.HandlerClient(app_id, access_key)

using mqtt client

mqtt_client = handler.data()
mqtt_client.set_uplink_callback(uplink_callback)
mqtt_client.set_downlink_callback(downlink_callback)
mqtt_client.connect()

mqtt_client.send(“lgt92-public-gps”, payload, 1, False, “replace”)
time.sleep(600)
mqtt_client.close()