Within Settings > General, set Send confirmation emails to new clients = Don't send before clicking Save at the bottom of the page:
When a new client registers, they will see the following message:
Thank you for signing up!
We are not ready to accept bookings but we will send you an account when we are.
They cannot book until their account has been confirmed via email or by an admin.
If you want to allow a new client through to book, on the Clients page (filter for unconfirmed clients), click Resend Confirmation. This sends the client an email (with the subject 'Confirmation instructions') to verify their account:
Alternatively, open their record, click Tap to resolve on the email verification banner and choose Manually verify email:
Related articles
How to disable online booking - Stop/prevent clients from booking online for a shop or staff member.
How to hide a staff member from new clients - Prevent clients who registered after a set date from booking with certain staff members.