You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello.

USER: Ryan Jackson here.

ASSISTANT: How may I assist you?

USER: I am planning for a trip to Austin and I will be departing in the evening time. So can you book the flight ticket for me?

ASSISTANT: Sure, I am here to assist you. Please provide me your trip dates.

USER: The trip dates are from 19 Aug to 21 Aug.

ASSISTANT: May I know your source and destination airport codes?

USER: My airport codes are from PHX to AUS.

ASSISTANT: May I know your name?

USER: I am Ryan Jackson.

ASSISTANT: Thank you. Please wait for a while.

USER: Sure.

ASSISTANT: Sorry. As per your requirements, there is no flight available.

USER: Not a problem. Thank you.

ASSISTANT: You are welcome and have a nice day.