Azure AD External Identities (B2B) uses Monthly Active Users (MAU) billing. The SC-300 content explains that to enable MAU-based pricing, the Azure AD tenant must be linked to an Azure subscription so that usage can be metered and billed. The configuration is performed in Azure AD # External Identities # All settings # Linked subscription, where administrators associate the tenant with a subscription and resource group. Only after this association do External Identities sign-ins count against MAU rather than per- user licenses. Access reviews (A) and terms of use (B) are governance features that do not affect billing. User flows (D) are specific to Azure AD B2C and are unrelated to enabling MAU billing for B2B External Identities. The study guide highlights: "To use MAU billing for External Identities, link your Azure AD tenant to an Azure subscription so guest usage is charged per monthly active user." Therefore, the correct prerequisite to ensure MAU billing is configuring a linked subscription.