couple of things need to be set for it to work, but this is coming from a 920 user on AT&T
1: secure sim
2: wallet service activated by your provider (that was on my receipt when i got my secure sim, also, your provider handles everything from pasword resets to closing the account)
3: NFC on and tap to pay enabled in the NFC settings
4: setup your selected card. if using amex serve, make sure you either have some cash in the account, or allow it to withdraw from your debit card.
what could help out is knowing where the reader can see your phone's nfc (and if it can see it through a case if you have one) on the 920, the space between the rear camera and the top of the phone is what I place on the reader. if i center my phone, it will not detect it.
hope some of this helps