I've encountered the same issue while trying to update the vanity_url of an event via the Eventbrite API. After diving into the API documentation and running some tests, it appears that the API returns a 400 Bad Request error with the message "Unknown parameter" when trying to update the vanity_url.
Here's the error response I received:
Interestingly, the API documentation doesn't explicitly mention how to set or update the vanity_url, which leads me to believe that this attribute might not be directly editable via the API.
Given this, it seems we might have to manually set the vanity_url through the Eventbrite dashboard, as the API doesn't appear to support this feature.
If anyone has found a workaround or has more information on this, it would be great to hear your insights.