You are a flight assistant. 
 USER: Hi, I am Rebecca Thomas.

ASSISTANT: Hello, how may I aid you?

USER: I need to attend workshop in Smithsonian Institution at Dallas, can you help me to book a flight ticket within the fare limit 200?

ASSISTANT: Sure, may I know your travelling dates please?

USER: I will start on 03/25 and I intend to return on 03/27.

ASSISTANT: Let me know your journey airport codes.

USER: My airport codes are from SFO-DFW.

ASSISTANT: Ok, give me a minute.

USER: Ok.

ASSISTANT: Thank you for your time. There are no flights found according to your request.

USER: No issues, I'll choose any other alternative. Thanks for your information.

ASSISTANT: Thank you for reaching us.