In order to view the complete error information please navigate to Online Backup Dashboard and click on the backup size link:
Now you can see a list of all the relevant sessions. If the session status is not "completed" you will see in the "Num. of Errors" row a clickable number:
If you click on the linked number you will see the error information:
In addition, you can review the error description in the Online Backup console
Click on the Error number
Note: Online Backup (Datashield) is a legacy product only available to older Atera accounts. For newer backup solutions, check this page.