string $sanitized_user_login, string $user_email, WP_Error $errors )
Fires when submitting registration form data, before the user is created.
(string) The submitted username after being sanitized.
(string) The submitted email.
(WP_Error) Contains any errors with submitted username and email, e.g., an empty field, an invalid username or email, or an existing username or email.
Please note that this hook should never be used for custom validation. Any custom validation rules should be performed using the registration_errors filter.