Open the airplane configuration editor, and edit the "Parking Brakes test" field to be like this:
(L:A32NX_PARK_BRAKE_LEVER_POS,number)
Be sure you remove everything you have there, and have only this line. Then, RESTART Couatl from the GSX menu, and it should work.
The PMDG issue is completely different and it only need to use the custom parking brake in the PMDG correctly.