Agent is any person who is part of your support team, who typically responds directly to the customer queries. Sub user could be any department who has partial access to content.
Let’s say tech team has access to API, Finance team to payment related queries and marketing team to the offers and promotions. Each department could be a sub user. The admin can control the access of each user to the content that’s visible.
To know how to add agents and sub user to Voice account, read our Voice Documentation.