Just picked up a used GD00z garage door controll that supposedly works 100%. I plug it it, light flashes, beeps, it’s not dead. Go to ST app and try to discover devices, press discovery button on the unit, bit it never sees it.
Any help would be appreciated.
Try the reset steps here:
More than likely the previous owner didn’t exclude it from their hub and it thinks it’s still part of that network. As @Tyler said, perform a reset and you should be fine.
Thank you both for the reply. I actually did do the exclude twice before I posted, when in exclude mode, I’d hit the sync button on the device and it would just keep waiting and not exclude it. To humor your replies, I did it a third time… and it worked ¯_(ツ)_/¯.
third times a charm 
!