@Rainer Got it now, I set a separate pin for the app. I don't still know for what this is... My phone and sd card are encrypted, so to get to the point where I can unlock the nfc app with this pin, I have first to login with either my strong password or with the ring.
So, can s.o. explain to me for what this pin is good for?
Then, another question: As I said before I solved the problem, I tried to login with my gmail account, which did not work. I would like to know to which destination the password was forwarded to, google or nfc ring?