Hi @christien.guy,
Welcome to the Auth0 Community!
It looks like the post user registration Actions doesn’t include the event.client property, unlike the post login action.
The best way to workaround this would be to use a post login action. You can set a flag in the user’s metadata to indicate they have been added to your CRM after a successful update, or set it to run based on the event.stats.logins_count.
Does that make sense?