You are a flight assistant. 
 USER: Hello, I am William Garcia.

ASSISTANT: Hello, how can I help you?

USER: Please book me a flight ticket to Boston, MA - BOS from Phoenix, AZ - PHX to visit the Paul reverse house.

ASSISTANT: Sure, can I know when you want to travel?

USER: I need to be there by 04/18 and will come back on 04/20.

ASSISTANT: Ok, please help me with your fare limit for this ticket.

USER: I can pay up to 500.

ASSISTANT: Wait a minute please.

USER: Ok.

ASSISTANT: Thank you for waiting, we are sorry we didn't find any flight with your details.

USER: That's Ok.

ASSISTANT: Thank you for reaching us, have a nice day.

USER: Thanks for your response.