Any jobs configured to backup groups fail with “A parameter cannot be found that matches parameter name 'GroupMailbox’”
To be able to backup group mailboxes with Veeam Backup for Office 365 version 2.0 a new permission is required. So, the job fails because the account used to add the organization has insufficient privileges to access the group mailbox. This applies to any type of job so long as the group mailbox is enabled for backup.
Add either Mailbox Search or Mail Recipients permission on the account used to add your organization as shown below: