The link in my "claim your US$40 reward now that you're back" email didn't work either but the USD 40 credit appeared in my credit card account a few days later. So give it a few days and check your credit card again.
It is the credit card entered when making the reservation rather than any credit card used at the hotel. I made a "no prepayment needed - pay at the property" reservation and it worked out fine with the USD 40 credit (even that I paid for the room in cash at check-out).
Last edited by SK AAR; Aug 7, 2017 at 10:23 pm
Reason: add. info