The error "Synchronization to our backup app has failed" occurs when you try to add a tenant to the Hornetsecurity 365 Total Backup which was previously added to the Altaro Cloud Management Console.
This means that if a customer has ‘example.com’ as an Altaro Office 365 Backup customer, then this tenant/domain cannot also be added to the Hornetsecurity Control Panel for backup purposes, whether as a standalone service (365 Total Backup) or a bundled service (Total Protection Enterprise Backup).
Currently we do not support migrating a customer from one platform to the other, however this is currently being worked on and should be possible in the coming months.