FWIW, I was trying to make a leisure reservation using a BCD provided by my company through Fond Perks. I kept getting the message "The rate code you entered requires a discount number". I ended up editing my Preferences, and entering the new BCD code there (replacing an older one), and also entered the name of my employer. After I did that, I was able to make the reservation and received the (greatly) discounted rate. The BCD code was prepopulated, so I didn't have to enter it.

I was logged into my personal Fast Break account the whole time.