Type in MQTT 3.1 2.3 ... Payload ... CONNECT

In the 2.3 Payload CONNECT paragraph, unqiue should be unique.

The payload contains one or more UTF-8 encoded strings. They specify a unqiue identifier for the client, a Will topic and message and the User Name and Password to use. All but the first are optional and their presence is determined based on flags in the variable header.