Since it has been confirmed that the broker connection works via MQTT Explorer, it can be assumed that the host is reachable and the credentials are valid. Given that the issue arises specifically when connecting to secure brokers, it is advisable to ensure the use of a valid CA root certificate in conjunction with the mqttclient command.
Further information on configuring the MQTT client in MATLAB can be found in the official documentation:
Additionally, a detailed MATLAB Central Answer provides guidance on obtaining a root certificate for use with api.thingspeak.com. This approach can be extended to work with the broker currently being connected to:
I hope this helps resolve the issue with connecting to the secure MQTT broker.
