Mqtt connection not authorized

I was trying to get familiar with the Platform by publishing some JSON Data with an simple mosquitto publisher via MQTT. But every time I am trying to publish I get the same error message:

Client MqttDevice sending CONNECT
Client MqttDevice received CONNACK (5)
Connection error: Connectin Refused: not authorized.
Client MqttDevice sending DISCONNECT

I’m using the given command from the docs:
mosquitto_pub -d -h -p 1883 -i MQTT -u jt -P testCredential -t telemetry -m ‘{}’

And of course I’m replacing the username and the password with my own.
Could the problem be the broker address: trincandodo.thinger? For HTTP i was using something like “” but that dose not work either here.