Hello everyone . I'm having trouble with Vapi sending incorrect date/time format , even tho i specify that both in the tools and the prompt , yet everytime it send the data via api it always got it wrong . i'm expecting anything like : 2025-11-11T10:00:00 (November 11, 2025 at 10:00 AM) and what i'm actually getting is just literal string {preferred_time} , just the place holder text . Can anyone help me with this issue ? Call ID : 019a6fee-7e5c-700c-9e05-ab9db53f2b64 . https://cdn.discordapp.com/attachments/1437640420841492600/1437640421764370603/Screenshot_2025-11-10_174348___preferred_date_error_2.png?ex=6913fa7a&is=6912a8fa&hm=65f70fe5704d1157ccc7b3197c98c850de05f784312806cc1ea64c4c3a1f9732& https://cdn.discordapp.com/attachments/1437640420841492600/1437640422452101232/Screenshot_2025-11-10_171147___Vapi_preferred_date_error.png?ex=6913fa7a&is=6912a8fa&hm=1db9099b68882eac2165882d30066a9f49bc0d62f5916f5350931a7d2382fe39& https://cdn.discordapp.com/attachments/1437640420841492600/1437640422955548682/Screenshot_2025-11-10_174548_preferred_datte_error_3.png?ex=6913fa7a&is=6912a8fa&hm=58c5d07a7414a09e6c43f56df7516d774ca4c4bb730e0490301264e23734dad5&

To ensure Vapi sends the correct ISO 8601 datetime, update your tool parameter description and prompt to explicitly require ISO 8601 format and use variable extraction. For example:

json
"preferred_time": {
  "type": "string",
  "description": "Provide the datetime in ISO 8601 format (e.g., 2025-11-11T10:00:00)."
}

Make sure your assistant prompt says: "Extract the user's preferred time and convert it to ISO 8601 before calling the tool." This helps the AI model output the correct format instead of a placeholder. For more, 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)

i tried and still didnt work

Modify the URL of the

check_availability

tool to exclude the variables. You can test if the endpoint works by using an API request tool like Postman and sending a test request to the shortened URL to see if it accepts the JSON data (like the same data the tool from VAPI sent). If you want help testing it, let me know.