VAPI check_availabilitycustom tool returns 'No result returned' - n8n workflow not executing either

Questions
1

I’m integrating VAPI voice AI with n8n for a roofing appointment system. The check_availability custom tool keeps returning “No result returned” error in VAPI.

Setup:
VAPI assistant with 4 custom tools pointing to n8n webhook
n8n workflow with router to handle different tool calls
Google Calendar integration for availability checking

Problem:
VAPI successfully calls the tool (I can see it in VAPI logs)
n8n workflow doesn’t execute at all (no execution logs)
Getting “No result returned” error consistently

What I’ve tried:
Verified webhook URL is correct in VAPI tool server config
Fixed tool schema (parameters were mismatched - had startDateTime/firstName instead of just service/date)
Fixed n8n routing logic (was comparing boolean to string)
Verified VAPI response format includes toolCallId and result
Checked all Respond to Webhook nodes

Current Status:
Tools are configured, n8n workflow is active, but the webhook never receives the calls from VAPI. Not sure if it’s a VAPI configuration issue, n8n webhook issue, or response format problem.

Any help appreciated! ::folded_hands::

2

Hey @imel !

Use postman or any other way to send a cURL request to your webhook and see if it works.

I tried to copy your code but fails in my canvas and nothing is rendering.

1 Like
3

Thanks for your quick response. This is what I have going on. My bad but I have zero coding skills and don’t know haow to share it but here’s a screenshot of the workflow. I can definitely screenshot every node if it was necesary. thnak you.

workflow json

Screenshot 2025-11-29 193626
Screenshot 2025-11-29 1936261299×654 101 KB

4

Hi. Is this using the prod webhook while the workflow is live? Method, GET or POST?

5

The first webhook is set to post using ‘respond to webhook node’
n8n Workflow json

Appreciate your time and help. thank you.

6

No worries man. It should be on prod if you’re testing. is it?

7

Yes the workflow is active and the link at vapi server is the production link.

8

Did you set the environment variable WEBHOOK_URL in your .env file or docker compose?

9

I am using the n8n Cloud version, not self-hosting. I do not have access to a .env file or Docker configuration. I am using the Production URL provided directly inside the Webhook node.

1 Like
10

Ok then…

The simplest way to check if your webhook is ‘alive’, just need a cURL request.

You can use postman or a CLI .

11

Your n8n webhook trigger is publicly since sent a curl request and got a 200 response with the headers specific to your url.

It means is a misconfigurations on the VAPI side.