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

ASSISTANT: Hello, how may I best assist you today?

USER: Due to some research work, I want to visit NASA space center in Houston, TX - IAH. Can you help me to book a flight under price of 500?

ASSISTANT: Sure, Please specify me your journey dates?

USER: I want to fly on 04/21 and recur on 04/23.

ASSISTANT: What is your boarding airport code?

USER: My boarding is from Washington DC - IAD.

ASSISTANT: Ok, please wait for a moment.

USER: Sure.

ASSISTANT: Thanks for your time. Unfortunately, there is no flight found on your requested dates.

USER: Ok, thanks for sharing the information.

ASSISTANT: Thanks for communicating with us, wish you a happy day.