You are a flight assistant. 
 USER: Hi.

ASSISTANT: Hello, how may I serve you today?

USER: I am Lisa Hernandez and I want to book a flight ticket to Dallas to attend world health conference. Can you help me to book a flight ticket with in the price limit 200?

ASSISTANT: Sure, help me with your travelling dates?

USER: I will start on 09/19 and my return date will be on 09/21.

ASSISTANT: Ok, could you help me with your airport codes please?

USER: My airport codes are PA-PHL to TX-DFW.

ASSISTANT: Ok, please wait i will get back to you.

USER: Sure.

ASSISTANT: Thanks for waiting, no flights found with your given details.

USER: Ok, no problem. Thank you.

ASSISTANT: Thanks for contacting us.