Adding Organizations with Modern App-Only Authentication
When you add an organization using the modern app-only authentication method, you are required to provide Azure AD application settings. Veeam Backup for Microsoft 365 uses such an application to establish a connection to your Microsoft 365 organizations with enabled security defaults and maintain data transfer during backup and restore sessions.
With modern app-only authentication, you cannot use Veeam Backup account; only communications through Azure AD application is possible.
Adding Microsoft 365 organizations using modern app-only authentication is not supported for Microsoft Azure Germany region. For limitations in Veeam Backup for Microsoft 365 functionality when protecting organizations with modern app-only authentication, see this Veeam KB article.
To add a new Microsoft 365 organization to Veeam Backup for Microsoft 365, do the following: