Not sure what might be wrong. I’ve found the setup process can be a bit finicky. I have a dishwasher in each of 2 locations and it took me quite a long while to get each one correctly set up in openHAB.
Have you tried putting the binding in DEBUG mode to see if it logs any additional details that might be helpful?
Have a look in the openHAB logs, there should be additional details why it failed. Look for a log message starting with Failed to complete authorization (it is logged on warning level so there is no need to increase the log level).