Every Rebrandly account has a default workspace: the Main Workspace.
Most API calls about Links, Tags, Scripts and Domains will default to the main workspace if you don't specify a different workspace.
See Get started section for info about how to specify a different workspace for resources you are going to create, edit/delete or just list.
You can create workspaces in your Rebrandly dashboard and invite teammates to collaborate.
Each workspace will allow you to define which subset of your domains your teammates will be able to use to shorten URLs.