iPhone owners who recently restored their devices to factory settings woke up to discover that they could no longer add their cards back to Apple Pay. The issue was a mystery even to Apple, which prompted the company to issue replacement phones.
Between the time this problem first hit the wires and now, Apple seems to have resolved the flaw remotely.
Identical stories from everyone
It isn’t clear what caused the problem, but almost every user writing in this forum thread reports an identical scenario: factory reset led to the inability to re-add credit/debit cards to Apple Pay.
Apple doesn’t monitor its forums, at least not in a very active manner, and therefore has not issued any clarification as to why Apple Pay refused to take cards on factory-reset devices between December 13 and now. The banks could also be to blame. The likelihood of this being tied to their security measures is high.
All’s well that ends well
The “greened” answer in the thread – the officially correct answer to the question asked by OP – reads: “I just tried to add a card to Apple pay and it worked. Seems like apple fixed the issue. so I recommend you all to try to add a card to your passbook and see if it's working.”
This person notes that he/she refused to get a replacement phone because Apple would not replace it with a brand new model, but one that had been refurbished. Starting with December 31, the problem seems to have been addressed for everyone.