We understand and appreciate the complexities of Multisite instances. For the Sucuri Platform, you must sign up for a plan that covers all of your domains. Yes, we understand they share the same core, but they don't always share the same theme. Depending on your configuration, you could have multiple unique domains pointing to one install. Those distinct domains could be affected or blocklisted, and without directed knowledge of the domains we'd be none the wiser. To address this, a license is required for every domain to ensure we go through each one individually. Due to the nature of Multisite configurations, you cannot effectively sign up to cover just one domain without touching all of the others.