Google Oauth adding a block and display text if the account doesn't already exist

Hello,

For my app, users have to go through an onboarding process before creating an account. I recently noticed that if a user goes through the member login flow, and signs in via Google, they can bypass the onboarding process. I found a way to prevent it and immediately delete the account due to all the missing information from bypassing onboarding but I wonder if there is a smarter way to do this. Additionally, it would be great to display a specific message to the user so they understand what happened, but since it refreshes the page, I can’t think of any constraint to use because the user has been deleted and no longer exists. Any thoughts on this would be helpful, thank you!