When you search for flights by creating an offer request, we'll give back a series of search results which we call "offers".
Each offer has an `expires_at` timestamp. After this time, you'll receive an error if you try to book it (i.e. create an order). A while later, it will be deleted from our database completely.
The "lifetime" of an offer (i.e. the time between when you search and the `expires_at` timestamp) can be different for different airlines, but it is usually around half an hour.
If you want to book an expired offer, you'll need to start again with a new offer request to get a fresh offer.
We're thinking about adding a way to refresh expired offers without searching again. If you'd be interested in this, please get in touch.