async def handle_transfer(room_name: str, participant_identity: str, assistant: VoiceAssistant) -> None:
    try:
        transfer_number = os.getenv('BILLING_PHONE_NUMBER')
        if not transfer_number:
            raise ValueError("Billing phone number not configured")

        if not transfer_number.startswith('+'):
            transfer_number = f"+{transfer_number}"

        await assistant.say("Transferring you to our billing department. Please hold.", allow_interruptions=False)

        livekit_api = api.LiveKitAPI(
            url=os.getenv('LIVEKIT_URL'),
            api_key=os.getenv('LIVEKIT_API_KEY'),
            api_secret=os.getenv('LIVEKIT_API_SECRET')
        )

        transfer_uri = f"tel:{transfer_number}"
        transfer_request = proto_sip.TransferSIPParticipantRequest(
            room_name=room_name,
            participant_identity=participant_identity,
            transfer_to=transfer_uri,
            play_dialtone=False
        )

        logger.info(f"Initiating transfer for participant {participant_identity} to {transfer_uri}")
        await livekit_api.sip.transfer_sip_participant(transfer_request)
        await asyncio.sleep(2)
        await assistant.cleanup()
        logger.info("Transfer completed, exiting process")
        os._exit(0)
    except Exception as e:
        logger.error(f"Transfer failed: {e}", exc_info=True)
        await assistant.say("I apologize, but I couldn't transfer your call. Please try again later.", allow_interruptions=True)

@assistant.on_message
async def handle_message(message: str):
    message = message.lower().strip()
    
    if message in ["yes", "yeah", "sure", "okay", "correct", "yep"]:
        participants = list(ctx.room.participants.values())
        if not participants:
            logger.error("No participants found in room")
            await assistant.say("I'm sorry, but I cannot process the transfer at this moment.", allow_interruptions=True)
            return

        participant = participants[0]
        logger.info(f"Attempting transfer for participant: {participant.identity}")
        await handle_transfer(ctx.room.name, participant.identity, assistant)
        
    elif message in ["no", "nope", "not now", "nah"]:
        await assistant.say("Alright, is there something else I can help you with?", allow_interruptions=True)
    else:
        await assistant.say("Would you like me to transfer you to our billing department? Please say 'yes' or 'no'.", allow_interruptions=True)