Can't enable developer mode SmartTV

I am directed to activate Developer Mode from Apps panel on TV
i try to do this using the remote that came with TV for my model TV: QN55Q8FNB
Ser: 07AK3CYK700263A
The tv is connected to a wi-fi network, on which the development laptop is also present
I don’t believe the tv is ‘legacy’ - It’s manufacture date, indicated by serial # is 7/2018
Additionally, there is no explicit ‘smart hub’ - the Home button just pops up a menu bar at bottom of the screen where I can select the Apps panel
Following instructions to go to the Apps panel and enter “12345”…
i enter 1 2 3 4 5 (Done)
Nothing happens (no developer mode popup)
I have checked for updates to the firmware. It says i am current (Software Ver T-KTM2AKUC-1310.4, BT-S)

could you provide a screenshot or more details about how the “internal error” message shows up?