The items which you receive from the Fortune Crates are not added to your inventory, but rather they fill a slot on your Airship. Once you have filled all the Airship slots with Fortune Crates you can either claim the displayed items along with a Mystery Crate by purchasing the offer or you can recycle its content. Recycling the content gives you a small amount of loot and sends the Airship away until more Fortune Crates are found.
It is possible to claim the Airship loot before all the slots are filled, but in that case, the Mystery Crate is not included in the offer. Please note that the only way to reveal the contents of a Mystery Crate is to purchase the items stored in a full Airship.
It is possible to claim the Airship loot before all the slots are filled, but in that case, the Mystery Crate is not included in the offer. Please note that the only way to reveal the contents of a Mystery Crate is to purchase the items stored in a full Airship.