I just sold my H9 and forgot to unregister it before shipping. Now I am unable to unregister it w/o the physical device present via the H9 Control app. I am also unable to unregister it through the Web portal.
Right, you need to have the H9 connected to the app to deregister it. We do things this way, because the registration of the H9 is one of the most important safety mechanisms we have to prevent just any from connecting to your H9 over Bluetooth from H9 Control and changing its settings while you're using it. But in any case please send an email to firstname.lastname@example.org with the serial number of the H9 you would like deregistered.