Calendly Scheduling API returns HTTP 200 with error & shifting available slots on retry

We are integrating the Calendly Scheduling API with our agentic system and are facing unexpected behavior while booking meetings.

Request Payload

{

"date": "2025-12-19",

"time": "02:00",

"email": " [removed by moderator] ",

"name": "name"

}

Response Received

• HTTP Status: 200

• Response Body:

{

"status": "error",

"message": "I encountered a system error while booking. I will have a specialist call you to confirm.",

"meeting_url": "",

"scheduled_time": ""

}

We are unsure why the API returns HTTP 200 while the response body indicates an error.

Slot Availability Issue

When testing different times:

• Request with time = 06:00 returns: “The slot is not available, you can book a slot from the 06:30, 07:00, 07:30”

• Retrying with time = 06:30 returns: “The slot is not available, you can book a slot from the 07:00, 07:30, 08:00”

Each retry shifts the suggested availability forward, even though we are selecting from the suggested slots.

Expected Behavior

Our logic is:

1. If the requested slot is unavailable

2. Fetch the next 3 available slots

3. Suggest those slots to the user

However, the availability window appears to change with each request.

Questions

1. Why does Calendly return HTTP 200 with a logical error in the response body?

2. Is this behavior related to timezone handling, minimum scheduling notice, or buffer rules?

3. Should availability be re-fetched on every retry, or cached?

4. Is there a recommended approach to consistently retrieve and lock the next available slots?

Any guidance or best practices would be greatly appreciated.