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! 🙏 https://cdn.discordapp.com/attachments/1444116914153722009/1444116914426347683/Screenshot_2025-11-28_101705.png?ex=693ff96e&is=693ea7ee&hm=6d6fe5b5982c17b6a6babe7ae08a53d429ce12599e8de24b4cf4f8e622c48ab6&

Hi Seda, Thanks for the detailed breakdown — that helps a lot. To understand why VAPI is returning “No result returned,” could you share the exact tool response payload that your n8n webhook is sending back to VAPI? Specifically, we’d like to see the raw JSON your server returns so we can verify the structure, including: -

toolCallId

-

result

- Any wrapping fields your workflow might be adding Once we have that, we can pinpoint whether the issue is related to formatting or something else in the tool chain. Thanks in advance!

Hi, thanks for helping. I'm building this with n8n using a no-code workflow, so I'm not 100% sure on the terminology, but I went into my execution history to find the latest execution from the check_availability output. I'm using custom function tool for Google calendar. Here is a screenshot of the final 'Respond to Webhook' node in n8n, and here is the JSON code it generated: Does this look like the correct structure for the toolCallId and result? https://cdn.discordapp.com/attachments/1444116914153722009/1445937675919167609/Screenshot_2025-12-03_174233.png?ex=693229e6&is=6930d866&hm=1b30a98ecbab223f74da9b99e6c012328fa9fe1cfe7106e6e51cbb58d3cfa120&

The response format looks correct 👍 Can you double-check that the

toolCallId

you return from n8n exactly matches the

toolCallId

sent by VAPI in the original tool call request? If the IDs don’t match 1:1, VAPI will show “No result returned” even if the payload structure is valid.