TransportInvalid error when establishing a secure connection using QtMqtt

I am using the [open source QtMqtt module |https://github.com/qt/qtmqtt] to establish a secure connection to AWS broker. I have been following Cloud providers and telemetry via Qt MQTT blog post and cloned[ QtMqtt cloud connectors repository|https://github.com/mauricek/qtmqtt_cloud_connectors]. 

Whenever I try to establish a secure connection using the code I cloned from the repository mentioned above I get the error message 

I also tried to modify the code and used test.mosquitto.org as a broker with port 1883 (unsecured connection) and I was able to have a successful connection. But, when I try test.mosquitto.org with port 8883 and their certificate for a secure connection, I got the error described above.

I tried that on both MacOS 10.15.4 and Windows 10 using Qt 5.14.2