The IDC Platinum website is here: https://www.americanexpress.com/en-xb/travel/discover/ It does not appear to display prices or process reservations, but this may change when you login. FHR online bookings were implemented for USA cardholders in 2010, and for Canada in 2014, but it's not surprising that not all markets have this feature. If the Centurion concierge is the correct booking channel for FHR with your card, you could ask them to see if the property will honor the USA rate for your stay.