Multi-turn tool-use scenario.
Tools involved: TravelAPI

User requests (one per turn):
user: I just graduated and plan on traveling for alumni meetups. I'm really curious which airports are around cities?
user: cities like Rivermist and Stonebrook, can you find some for me
user: Great! I'll be flying out of Rivermist soon. Could you help me figure out how much it would cost to go from there to Los Angeles on August 15, 2024, in business class? I've just checked the nearest airport for Rivermist without mentioning it, as you already know it.
user: I got some substantial savings from the last trip! Now, let's set a budget limit of $1500 for my future travel planning using my secure token ABCDE12345.
user: Now, with the newly set budget and using card with id 1432 out of my available cards, I'd like to book that business-class flight from Rivermist to Los Angeles on August 15, 2024, utilizing my access token ABCDE12345. You already know the travel cost!
user: Lastly, will you fetch the invoice for that recent booking using my access token ABCDE12345? I need a summary for my records.

Expected function call sequence:
TravelAPI.list_all_airports
TravelAPI.get_nearest_airport_by_city
TravelAPI.get_flight_cost
TravelAPI.set_budget_limit
TravelAPI.book_flight
TravelAPI.retrieve_invoice