If any GCP lab prompts you for validation, please choose the "confirm your recovery email" option. (Note: please do not choose any other option. You may have chosen "Get verification code at XXXXXXXXXXXX" which would require you to enter the code using a phone number you don't have).
Once on the next page, please enter the recovery email given in the lab credentials for the session.
As a reminder, the recovery email is located on the lab instructions page under the GCP credentials that were generated for your attempt. These are changed after each lab.
If the issue still persists after all the above steps, please email email@example.com and send them a screenshot of the error you were seeing as well as the credentials being entered.