We recently switched the primary domain for this support system from fandom.zendesk.com to support.fandom.com, to reduce visitor confusion.
If you're running into an "Invalid Authenticity Token" error when trying to log in to Fandom Support, this may be due to outdated browser cookies related to this switch.
For assistance with this issue, please see this Zendesk help page. (The Fandom Support system uses Zendesk software.)