Need help with checkAvailability tool in Vapi

I built an assistant in Vapi, and everything is working great except the Check Availability tool. It isn’t retrieving data correctly. It doesn’t recognize busy or booked time slots on the calendar and shows them as “free” even when there’s already an appointment at that time.

Note: There’s nothing wrong with the prompt.

Here’s what the tool returned:

Response Details

{

"busy": [],

"free": [

{

"start": "2025-12-26T14:00:00.000Z",

"end": "2025-12-26T15:00:00.000Z"

}

]

}