I have the excact same problem as described here.
Nexus 5 (also tried Xperia Z2) - Stealth bomber ring. Get the same "ALERT Not NFC ring", and therefore can't register my ring.
Other than that, I really love my ring! :-)
(I was to late for Kickstarter, but preordered through the website)
I forgot to say that I had the get-started link :-) (Have overwritten one of them now though)