As noted above, they supposed to be presented with a valid Reserve Card and are meant for guests other than the cardholder.

https://www.americanexpress.com/us/c...-0#offer-terms

"To redeem, the Card Member must present his or her valid Card, same-day Delta or Delta partner boarding pass, and government-issued I.D. to the Delta Sky Club ambassador. The Basic Card Member must be present in order to use the one-time guest passes and all eligibility rules of the Delta Sky Club benefit apply. The guests must be traveling on a same-day Delta-marketed or Delta-operated flight. The Card Member may only use two one-time guest passes per Delta Sky Club visit. One-time guest passes are non-transferable, cannot be assigned or sold, and have no cash value. Benefit valid only at Delta Sky Clubs. Partner lounges are not included. "