You can assign multiple domains to your Website Builder site. The domains display the same site as the primary domain associated to the Website Builder account.
Assigning multiple domains to a single Website Builder site is called domain aliasing. Aliasing is preferred to forwarding domains to your site as forwarded domains are less searchable than an aliased domain.
You can only alias domains that are available within your customer account. Please allow up to 48 hours for the aliased domain to display your site.