Citibank cardmembers would have received a mailer regarding the Citi PayAll service, that allows for payments to various payees while earning miles in the process.
This is very similar to the UOB PRVI Payment Facility, except that in this case, you must specify a payee who will receive the amount charged to your card.
Miscellaneous payments, such as those to educational institutions and monthly rentals, may be explicitly excluded from earning points or miles on most credit cards. However, for a nominal fee, you can still earn miles for such payments using Citi PayAll. The actual fee that is payable over and above the amount transacted will be made known to you before you make your payment.
Here is an illustration of how many miles you can earn with Citi PayAll. Note that this assumes a 1.2 mpd earn rate, when you use your Citi PremierMiles card. Presumably, using your Citi Prestige card will allow you to earn 1.3 mpd.
Full terms and conditions can be found here.