This read-only DisplayString holds the human-readable error text the Radio Master most recently sent to a Radio Slave in an Authorization Invalid message, returning an empty string if no such message has been transmitted. It gives descriptive context to pair with the numeric cwrBpiRmAuthInvalidErrorCode for that same rejection event. For example, an admin auditing why the master rejected a particular slave would read cwrBpiRmAuthInvalidErrorString for the plain-language explanation transmitted to that radio.