Jul 11 • Support Needed 💻
Need Help in Voice Agent - Retell AI + Cal.com
Hi everyone,
I’m working on a Retell AI voice agent that integrates with Cal.com to check and book appointment availability.
The Issue:
When a user says something like:
“Book an appointment tomorrow at 3 PM”
The agent is not converting that into a full ISO timestamp like 2025-07-11 15:00.
Instead, it’s sending "start_time": "tomorrow 3:00" to the check_availability function, which causes errors or broad time range behavior.
I want it to:
Parse “tomorrow 3 PM” into → 2025-07-11 15:00
And end_time as → 2025-07-11 15:30
Tools I'm Using:
Retell AI (Voice Agent running GPT-4.1 mini)
Cal.com for real-time booking availability
Function call: check_availability
My Current Prompt Logic:
Ask for their preferred date and time.
If the user specifies a time (e.g., "tomorrow at 1 PM"), convert it into a precise 30-minute slot.
Call the function check_availability with:
- start_time: the exact time requested in ISO format (e.g., 2025-07-11 13:00)
- end_time: 30 minutes after the start_time
Do NOT use the full-day time range unless no time is provided.
What I Need Help With:
How can I ensure the model always resolves phrases like “tomorrow” or “next Monday” into full ISO timestamps?
Is there a better prompt or formatting method that works with Retell and GPT-4.1 mini? Has anyone already solved this with Retell + Cal.com?
Any guidance, working examples, or fixes would be appreciated.
Thanks,
Sukumar
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3 comments
Need Help in Voice Agent - Retell AI + Cal.com
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