Multi-turn user requests:
user: As I'm mapping out the logistics for my forthcoming business journey, I require an estimate for airfare traveling from the first to the second airport in your inventory, all set for December 15th, 2024. My travel funds should not exceed $2000, and I'll use my designated access code, 12345-67890. Could you retrieve this information for me?
user: Relating to the travel itinerary I'm arranging, I would like to secure travel insurance with a fee of $300 linked to booking code d184e2c0-2ebb-4f39-a525-d5e01b67dc6c. I'd prefer to utilize the payment method associated with card ID '0001'. Kindly finalize this with my access code 12345-67890.
user: Could you assist by procuring the invoice for my reservation? I need to review the specifics to confirm precision, tapping into my access code 12345-67890 for verification.

Ground-truth function call sequence:
TravelAPI.list_all_airports
TravelAPI.get_flight_cost
TravelAPI.set_budget_limit
TravelAPI.purchase_insurance
TravelAPI.retrieve_invoice
MessageAPI.send_message
MessageAPI.delete_message