Currently for our Google Workspace Backups, any Sub-Domain backups need to be created on the backend by our Development Team.
To get these Sub-Domains backed up, please provide us with the usual Google Workspace Super Admin credentials and a list of all the Sub-Domains that need to be backed up. With just that information, we can create all the backups for the Sub-Domains.
Alternatively, if you do not want to provide us with credentials for the Google Workspace Super Admin account, create the Workspace backup using the Super Admin account and let us know when it has been created. The backup that you have created will not include any of the sub-domains but after reaching out to us, we will create and add those to the already existing backup.