Hello dear VAPI team, We are building a booking system using your web widget. Our workflow has two parts: A user talks to our Vapi assistant to schedule an appointment. This triggers a tool call to our backend. After the voice interaction, a pop-up form appears on our website for the user to enter their phone and email to confirm the booking. This form submission also goes to our backend. Our goal is to reliably link the initial voice booking (Step 1) with the contact details from the form submission (Step 2). We noticed that the Vapi widget sets a cookie named callId in the browser. Our plan is to read this callId from the HTTP request headers on both backend requests to act as our unique session identifier. Our question is: Can we reliably use this callId cookie for session management? Is it a stable feature of the widget that we can depend on?

Use the callId from webhook payloads rather than browser cookies: 1. **Capture callId from webhook**: Use [req.body.call.id](http://req.body.call.id) in your tool call webhook 2. **Store session data**: Link booking details to this callId in your database 3. **Bridge to form**: Pass the callId to your form through: - URL parameters - Session storage - Hidden form fields - Return it in the tool response This approach is more reliable than depending on browser cookie mechanics and gives you full control over the session management flow.