An even more accurate Big Mac example would be McDonald’s is giving away Big Macs in locked boxes placed at every street corner, but you need to pay for the key

An even more accurate Big Mac example would be McDonald’s is giving away Big Macs in locked boxes placed at every street corner, but you need to pay for the keys to the box. So you let people know that the keys that they paid for earlier are still valid and can still be used, and you show them how. McDonald's cries foul because they just expected people to buy new keys.