Why Does My Workflow Return a 404 Error When Activating Automatic Mode?

It sounds like the issue is related to how n8n configures webhook endpoints for automatic execution. When you run in manual mode, n8n doesn't register the triggers as webhooks. However, once you activate the workflow, it needs to expose a public endpoint for the RSS trigger, and a misconfiguration here can lead to a “Status code 404” error.

Here are a few things to check:

1. WEBHOOK_URL Setting
   Ensure that your n8n instance’s public URL is set correctly via the WEBHOOK_URL environment variable. If you’re running behind a reverse proxy, the URL must be accessible externally (and use HTTPS if needed). Without this, n8n might generate webhook URLs that cannot be reached or registered, resulting in a 404 error.

2. Reverse Proxy Configuration
   If you’re using a reverse proxy (e.g., Nginx, Apache, or Traefik), verify that it is configured to forward both HTTP and websocket traffic correctly. Incorrect proxy settings can lead to the webhook calls not reaching n8n.

3. Testing the Public URL
   Double-check the webhook URL that n8n is attempting to use by:

   • Looking at the logs or execution details in the Editor UI.
   • Manually navigating to the expected webhook endpoint from an external network to see if it’s accessible.

4. Node-Specific Requirements
   Some triggers might behave differently when activated automatically compared to manual executions. Review the configuration of your RSS trigger to ensure that you haven’t overlooked any settings intended for production mode.

By verifying these configurations, you should be able to pinpoint why the webhook (and thus the trigger) isn’t being registered properly when the workflow is activated. This approach follows the troubleshooting steps outlined in the n8n documentation for managing workflow executions and webhook configurations.