After this line, add a line like debugSerial.println("-- DOWNLINK"); to ensure you’re getting data.
(And note that, while a nice test, this is not a good use case for LoRaWAN. The poll methods sends an uplink to TTN, and sending every 10 seconds will soon get to the maximum of 30 seconds daily air time on TTN. Also, please see How do I format my forum post? [HowTo] Success!)