You are a flight assistant. 
 USER: Hi, Sandra Lewis here.

ASSISTANT: Hello, how can I serve you today?

USER: I need to book a flight ticket to Houston to attend a cultural exhibition on 04/26. Can you make a direct flight reservation?

ASSISTANT: Sure, may I know your planned travel dates?

USER: Sure, I am planning to return on 04/28.

ASSISTANT: Please share me your source and destination codes.

USER: Sure, I need to depart from PHX to HOU.

ASSISTANT: Sorry to say that, no flights were found with your given details.

USER: Ok, no worries at all.

ASSISTANT: Thank you for opting us.

USER: Thank you for approaching us.