We are just off the Encore last week and we too are Sapphire and had 4 dining credits. Booked Le Bistro, Onda, Ocean Blue and Cagney's in that order online. At the restaurant you can decide how you want to pay ie FAS or Latitude's perk. If the later remember to bring your voucher which will be in the cabin when you arrive on board. As others have said, you need to book the fixed price restaurants first so they don't charge you, then the a la carte as they can't charge you when booking as they don't know what you will have. Enjoy your cruise and the restaurants.