### Answer The built-in

book_appointment_cal

function has limited functionality and doesn't support adding custom notes or additional fields like meeting notes that only the calendar owner can see. [(1) ]() [(2) ]() To add notes or other custom variables to calendar appointments, you'll need to create a custom function instead of using the pre-built

book_appointment_cal

tool. The built-in function only handles basic booking parameters like time, timezone, name, and email. [(3) ]() For more advanced functionality such as passing notes, custom fields, or meeting descriptions, you should integrate a custom tool that directly calls the Cal.com API with the additional parameters you need. [(2) ]()

​ To learn more, see the sources I considered: [[1] book_appointment variable](https://discord.com/channels/1186424376300679209/1256246690118242364) [[2] calendar appointment booking through retell](https://discord.com/channels/1186424376300679209/1250814023067500657) [[3] Book Calendar](https://docs.retellai.com/build/book-calendar) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

Thanks for the feedback, glad I was helpful.