Hi @a.bilani
Welcome to the Auth0 Community!
Thank you for posting your question. Unfortunately, the event request.query property is not available in the pre-user registration Action. It’s available in the post-Login Action only. You can read more about that here → Pre-registration Action with event.request.query
I would encourage you to create a new topic in the Product Feedback category, explaining your use case and desired solution. Make sure to vote on your card!
Thanks
Dawid