I've been troubleshooting this error for some time now, and i'm not sure where to go from here, i've set a server URL in my phone number and I return a session_uuid variable so that I can see it in my prompt (which is now {{session_uuid}} and as an example i've set that as 1234abcd), which I can see, but I am still unable to add it into the API Request URL for some reason, why is this happening? @User if its needed here is my call id as an example: 1db52f15-1a7e-4a37-94b9-96c99d748c2d https://cdn.discordapp.com/attachments/1419633093538615336/1419633094805422092/Screenshot_2025-09-22_at_11.31.18.png?ex=68d277d9&is=68d12659&hm=c6dcc8ee1363eb35d61affe743c8197e436723322dbe190d105e6809e0568f11& https://cdn.discordapp.com/attachments/1419633093538615336/1419633095241498717/Screenshot_2025-09-22_at_11.30.44.png?ex=68d277d9&is=68d12659&hm=302c40ee9ce7996607bbe9da763e3bc6746db78c4ad2c518682a11c9b3bbe424&

Suggestion: Make sure the

session_uuid

variable is extracted and available before the API request node runs. In your workflow, add a variable extraction step or validation prompt prior to the API request, and confirm in your Call Logs that

session_uuid

is present in the variables list at that point. Example node prompt for extraction:

yaml
Extract the session UUID from the server response and store it as `session_uuid` before the API request node.

Then, use the URL:

https://your-endpoint/answer/{{session_uuid}}

Check the Call Logs to verify the variable is set before the API call—if not, adjust the workflow order accordingly. [See debugging steps](https://docs.vapi.ai/debugging#check-logs) Source: - [Debugging voice agents](https://docs.vapi.ai/debugging)

But it's already coming through the variableValues in the assistantOverrides

Hi mm, To use dynamic variables in your Vapi assistant, you need to incorporate them into your phone call setups or API requests by including them in double curly braces, e.g.,

{{name}}

. Here's a quick guide on how to include dynamic variables in API requests: 1. Prepare Your JSON Payload: - Include these key-value pairs:

json
     {
       "assistantId": "your-assistant-id",
       "assistantOverrides": {
         "variableValues": {
           "name": "John"
         }
       },
       "customer": {
         "number": "+1xxxxxxxxxx"
       },
       "phoneNumberId": "your-phone-id"
     }

- Replace

"your-assistant-id"

,

"+1xxxxxxxxxx"

, and

"your-phone-id"

with your actual assistant ID, customer's phone number, and registered phone number ID. 2. Send the Request: - Use the JSON payload to make a call to the

/call/phone

endpoint through your preferred method, like an HTTP POST request. Ensure that you set the necessary headers for authorization. You can find detailed instructions in the [Vapi Documentation on using dynamic variables](https://docs.vapi.ai/assistants/dynamic-variables). Let me know if you need further clarification or assistance with specific issues in your setup.