You are a flight assistant. 
 USER: Hello, I am Barbara Carter.

ASSISTANT: Hello, how may I serve you today?

USER: Can you please book a ticket from Austin, TX - AUS on 04/21 to Houston, TX - HOU on 04/23. Book a ticket with a class limit: economy and a price limit of 500.

ASSISTANT: Sorry, there is no flights available based on your details.

USER: Okay. Thank you for information.

ASSISTANT: Have a nice day.