Hello everyone, unfortunately I have a small problem. I put together an AI voice with a YouTube video. I followed it exactly as in the video. However, when the assistant is supposed to check the calendar to see if the appointment is still available, it only sends me an error message with the following: “Axios Error: error code: ERR_BAD_REQUEST, error message: Request failed with status code 404 response status: 404 response data: [{“code”:404,“message”:“1”,“hint”:“2”},“The requested webhook “964a0d19-194e-4a3e-afce-08d6b252805d” is not registered.”,“Click the ‘Execute workflow’ button on the canvas, then try again. (In test mode, the webhook only works for one call after you click this button)”]”
Unfortunately, I don’t know how to fix this problem. Has anyone had experience with this?
Good news, this is not a Retell problem. That error is coming from n8n.
n8n gives every webhook two URLs. The test URL only works once, right after you click “Execute workflow” on the canvas. The production URL works every time, but only once the workflow is switched on. Right now your agent is calling the test URL, so it stops working as soon as that one-shot window closes.
The fix: open your workflow in n8n, click the Webhook node, and copy the Production URL (it has /webhook/ in the path, not /webhook-test/). Then toggle the workflow to Active with the switch in the top right. Paste that production URL into your Retell custom function in place of the test one. The calendar check should then work on every call.
If it still 404s after that, double check the workflow is saved as Active and the URL matches exactly.
Hey Pascal, don’t worry this is actually one of the most common stumbling blocks when setting up an n8n webhook for the first time!
The 404 error isn’t a problem with your code or your Retell setup. It happens because n8n treats Test URLs and Production URLs completely differently. Right now, your Retell agent is pointing to n8n’s Test Webhook URL. In n8n, a test webhook is completely temporary and single-use; it only activates for a few seconds right after you click the “Execute Workflow” button on your canvas and shuts down immediately after receiving its first payload. If your Retell agent calls it outside of that brief window, n8n returns a 404 because the listener is literally turned off.
To fix this so your AI assistant can check the calendar automatically 24/7, you just need to switch it over to production mode. Here are the exact steps to resolve it:
Grab the Production URL: Open your Webhook node inside the n8n workflow editor. Switch the URL toggle from the “Test” tab over to the “Production” tab, and copy that live URL.
Update Retell: Go back into your Retell AI dashboard, open the custom function or subagent tool handling your calendar booking, and replace the old test URL with this new Production URL.
Turn the Workflow ON: Go back to your n8n canvas and toggle the active switch in the top-right corner from Off to ON.
Once you flip that active switch, n8n will keep the webhook registered permanently in the background. Your Retell agent will be able to check calendar availability on the fly without hitting that 404 error again.
Give that a shot, and let us know if your agent successfully books the appointment!