Q:

Unable to Install Microsoft Azure Backup Server

I've been having a problem for the past two days trying install Microsoft Azure Backup Server... I'm very close. 
The installation always fails to install the SQL server as shown in the image.
The error logs state:
On a domain controller, you cannot use the built-in Windows service accounts (Local Service or Network Service) as service accounts for Reporting Services

A:

Installation of Azure Backup Server on a domain controller is not supported - see this article.

I imagine this is primarily due to the reason you encountered, that installing SQL on a domain controller is also not supported. You will need to use another machine.

