The option to deactivate or delete a a particular brand is missing. Under Admin > Manage > Brands, the brand that can't be deleted or deactivated has a label for (Default) or (Agent) listed after it:
- Professional or Enterprise level plan with Multibrand Add-on
- Has at least two brands
It's expected that you wouldn't be able to deactivate or delete the default brand. If you need to deactivate or delete it you will first have to change the default to a different brand.
The (Agent) label shown on the other brand that can't be deactivated or deleted is there to indicate that it is set as your account's subdomain.
Your Zendesk URL has two parts: a subdomain name you chose when you set up your account (or a brand), followed by zendesk.com (for example: mycompany.zendesk.com). You can change the subdomain name for any brand on the Brands menu.
When your agents are logged into Zendesk they see one of your account's subdomains. This is called your agent route, and is always tied to one of your brands. You can select which brand agents see while logged into the agent interface using the drop-down menu under Admin > Settings > Account > Subdomain.