My gateway version is 1.11.47
I tried to use this sample code:
const string password = "ThisIsMySecretPassword";
const string applicationName = "TradfriControllerApp";
const string ipAddress = "192.168.0.230";
var controller = new TradfriController("Tradfri", ipAddress);
TradfriAuth appSecret = controller.GenerateAppSecret(password, applicationName);
It throws an exception: "Timeout Generating App Secret."
I've tried to increase the AckTimeout value but no luck.
Also the app writes this to the console:
"15:11:10 [DTLSClientChannel] Error - Failed to establish a DTLS session"
When checked the raw network data with Wireshark, this was the result:

