# Context I built an AI Voice Assistant (AI receptionist) on Vapi. Its tasks are to answer calls, help clients with their questions, check availability, and book or manage appointments. It has two tools: • Check Availability: checks available and busy time slots on the calendar. • Create Event: books and manages appointments. I integrated the calendar into Vapi through the Integrations tab, which has access to creating and editing events and checking availability. # Issue When the agent is asked to check availability, it doesn’t detect busy time slots on the calendar and shows a time slot as “free” even when there is already a booked appointment. The Check Availability tool does not parse the busy time slots. I will paste the response returned by the Check Availability tool when it is asked to check available times below: Response Details { "busy": [], "free": [ { "start": "2025-12-26T14:00:00.000Z", "end": "2025-12-26T15:00:00.000Z" } ] } # Notes - Nothing wrong with the system prompt of the agent - Calendar is Integrated and has been given permission to access - The time zone is America/Toronto and I’ve indicated this in the system prompt of the agent as well as in the description of the tools - I am not using any other platform like n8n, only Vapi for now Call ID I tried many times, here is one of them: 019b6715-236e-7cc7-aeff-da0b36e0b58f Feel free to ask for more details to solve this issue Thanks.

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Thank you for the detailed context. To help narrow down the issue: Are all your appointments/events that should be marked as "busy" on the same Google Calendar that the Check Availability tool is configured to query, and is the correct calendar ID set in the tool's configuration? If you're unsure, you can verify this in the Vapi Dashboard under Tools > [Your Check Availability Tool] > Configuration. Sometimes, events on a different calendar or a missing calendar ID can cause the tool to return empty "busy" slots even if appointments exist. Let me know what you find! Sources: - [Google Calendar Integration Documentation](https://docs.vapi.ai/tools/google-calendar) - [Custom Tools Troubleshooting](https://docs.vapi.ai/tools/custom-tools-troubleshooting) - [Debugging Guide](https://docs.vapi.ai/debugging)

Yes the correct calendar is integrated and the Calendar ID is correct too.

To ensure the Check Availability tool detects busy slots, double-check that your request includes the

timeZone

parameter (e.g.,

"America/Toronto"

) and that all datetime fields are in ISO 8601 format. Here’s an example payload:

json
{
  "startDateTime": "2025-12-26T14:00:00-05:00",
  "endDateTime": "2025-12-26T15:00:00-05:00",
  "timeZone": "America/Toronto",
  "calendarId": "primary"
}

Try updating your tool configuration with these fields and test again—timezone mismatches or missing parameters can cause busy slots to be missed. For more details, see the [Google Calendar integration documentation](https://docs.vapi.ai/tools/google-calendar). Source: - [Google Calendar Integration Documentation](https://docs.vapi.ai/tools/google-calendar)

Hi Zikrullah Dawran, Thanks — I reviewed the docs and your call logs context. To debug this quickly, please provide the exact tool call payload that Vapi sent for call_id 019b6715-236e-7cc7-aeff-da0b36e0b58f (the JSON arguments the assistant passed to the Check Availability tool). Key fields I need: - startDateTime (as sent) - endDateTime (as sent) - timeZone (if present) - calendarId (if present) If you can’t pull the payload, paste the tool call entries from Observe → Call Logs (tool request + tool response) for that call_id. Once I have that I’ll check for common causes (UTC vs offset, non-overlapping window, secondary calendar vs primary, or events marked private/tentative). Docs referenced: Google Calendar integration — https://docs.vapi.ai/tools/google-calendar

I am Having same problem, we're you able to fix this? And how you did it ? Explain in. Easy terms because vapi support always tells alot of complicated stuff when sometimes is pretty simple.