Hello @sinem ,
Thank you for the outreach and interested in HiveMQ!
One detail I wanted to confirm first is if TLS version 1.3 has been specified as the protocol version on your broker. This will ensure that TLS 1.3 is supported by the broker, as well. Some more information, including a code example using the HiveMQ Client, is available in this thread.
Best,
Aaron from HiveMQ Team