I've had this problem since updating to the "Galaxy Wearable" app (~2 months or so). My watch lost the ability to connect to my phone via bt. So, I did a factory reset on the watch, cleared the data on all watch-related apps on my phone, and did a full un-/re-install of the watch apps.
Now, when I run the Galaxy Wearable app, my watch model isn't listed on the "Pick your device" screen, so I select ""Mine's not here." It will detect my watch, but I can't select it because the button will first appear in orange/yellow but is immediately greyed out and can't be selected.
When I go into Bluetooth settings on my phone, the watch will be listed as an available device, but again, I can't select it and the phone will not pair with it. I've tried just about everything I can think of and a few things that I've read online, and nothing seems to work. Please help!