I have a workflow that is activated by changes to a Trello board. After triggering, it filters out events so that only a particular action (a card moving between two lists) is sent on to the rest of the workflow.
Sometimes when I restart n8n, this workflow fails to activate and gives this error message:
ERROR: Workflow could not be activated: 400 - "A webhook with that callback, model, and token already exists"
From what I understand, this is the error from the API call to Trello to set up a new webhook, which would then remain active and send events to the n8n workflow. It seems that after restarting n8n (such as after updating to a new release or updating packages on the server), n8n forgets it has a webhook already registered.
How does this work in the code?
- Does n8n request a new webhook each time the workflow is restarted? I
a. If so, does it make sure it has deleted the previous webhook when n8n is shutting down?
- Is it possible to re-use an existing webhook?
As a short-term workaround, I found that changing the name of the Trello Trigger node and saving/reactivating the workflow will register a new webhook that works, but this same issue eventually happens again after a few weeks.
EDIT: I’ve also been able to use the Trello API through Postman to look at the different webhooks registered, as well as go back and clean up the ones that n8n leaves behind.