After a two factor authentication service has been activated,  clients or admins can be forced to set up two-factor authentication before being allowed access to the Client Area or Admin Area:

1. Log in to your WHMCS Admin Area.

2. Go to Configuration > System Settings > Two-Factor Authentication.

3. Scroll to the Global Two-Factor Authentication Settings section.

4. Check the desired options.

5. Click Save Changes.

When a client or admin logs in, they will be required to set up two-factor authentication.