By default, Sucuri Firewall will only accept requests that go directly to the site(s) added on your dashboard, if you have other domains pointing to the same site (aliases) you can follow the instructions below to configure those.
How to Configure a Domain Alias
1) Click here to add the domain alias you want to add and then click on Add Domain.
2) Point both A records of the domain alias (example.com and www.example.com) to the Sucuri Firewall IP address of the site it is redirecting to.
There is a limit of 5 aliases, if you need more please open a support ticket with us.