You must show your activated AP with usage. I saw other threads where people are getting confirmation letters to use since they have upcoming trips. You might want to call the number and order now and hopefully speak to a human.
Here's the info from the passholder website.
Dining Discounts
Discounts are valid for purchases made by the Passholder only and valid Pass ID is required for redemption.
Disney Dining Experience
Receive $25 off the regular price of the Disney Dining Experience Membership.
Benefits include:
20% discount on all food and beverages at over 70 participating Resort hotel and Theme Park restaurants (discount is valid for a party of up to 10 Guests).
Resort and Theme Park parking for dining purposes
Invitations to special member-only food and wine events, winemaker dinners and celebrity chef dinners
And more!
Call (407) 566-5858 (Monday - Friday, 9 a.m. - 6 p.m. E.S.T.) for more information or to purchase your annual membership at the Passholder price of $50. The Disney Dining Experience Membership card is not accepted on holidays, including New Year's Eve, New Year's Day, Mother's Day, Easter, July 4, Thanksgiving Day, Christmas Eve and Christmas Day. Once you order your Disney Dining Experience membership card, please allow 2-3 weeks for processing.