I have missed an important step in the procedure Version 3.7.1 Add-on Package Install , and have added it now. Please carryout this important step given below:
Enabled UAT in piaware-config by setting uat-receiver-type sdr
sudo piaware-config uat-receiver-type sdr
sudo systemctl restart piaware
Without above step, piaware will keep its connection to dump978-fa closed, and as a result will not send UAT data to Flightaware.