Did some reading on the dorita980 project that supports this App - seems the process to get the robot password for the mqtt connection changed in the latest firmware (which of course applies to the J series)...
Now it has to go through the cloud API, as discovery mode cannot be retriggered once the robot has connected to wifi. The developer of dorita980 implemented a new command for this, and documented it here: https://github.com/koalazak/dorita980#how-to-get-your-usernameblid-and-password
Give that a try, update the configuration on your pi, and relaunch the rest980 service -- see if we get any further