Webhook/Form Trigger conflict: "The requested webhook is not registered" when testing identical workflows on two accounts simultaneously

Questions
1

Describe the problem/error/question

I am encountering an issue when trying to test the same workflow logic using two different accounts (users) on the same n8n instance.

What is the error message (if any)?

{
  "code": 404,
  "message": "The requested webhook \"post_method\" is not registered.",
  "hint": "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)"
}

Please share your workflow

To Reproduce

  1. I have two separate accounts/users.
  2. I created the exact same workflow in both accounts.
  3. The start node is a Webhook Trigger (or a Form Trigger).
  4. I click “Execute Workflow” (Test Mode) on both accounts so they are both waiting for a call.
  5. I send a request via Postman to the test webhook URL(It’s two different webhook URL).

Current Behavior

Only one of the workflows captures the request successfully. The other workflow fails immediately with the following error:

{
  "code": 404,
  "message": "The requested webhook \"post_method\" is not registered.",
  "hint": "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)"
}

Additional Information

  • This issue occurs with both the Webhook Trigger and the Form Trigger nodes.
  • This only happens in Test Mode. When the workflows are set to Active, both work as expected without conflict.

Information on your n8n setup

  • n8n version: 1.123.14
  • Database (default: SQLite): SQLite
  • n8n EXECUTIONS_PROCESS setting (default: own, main):
  • Running n8n via (Docker, npm, n8n cloud, desktop app): Docker
  • Operating system: Linux
2

I think is because that only one temporary webhook can be registered per instance. When multiple workflows hit “Execute Workflow” at the same time to register a webhook, only the most recently registered one will be active, and the others will fail.

3

That sounds like the likely cause, thanks.

However, since these are two separate workflows with unique IDs (and unique test-webhook URLs), I assumed they would be registered independently. Does the ‘Test Mode’ listener globally restrict the instance to only one active connection regardless of the workflow ID? And I’m wondering have you experienced this same issue?