After you invite a user to join your Dropbox Business team, they will be able to join the team. They can either transfer an existing account to a Dropbox Business account or create a new account using their work email address.
If they choose to transfer an existing account, they will be given the option to merge their existing files to the Dropbox Business account or create a new Dropbox Basic account for those files.
New members will automatically have access to content in the team space and any folder shared directly with them.
What if the member has a paid subscription?
When joining a team, if any member has a paid Dropbox subscription, they will receive a prorated refund for the unused period back to the card they previously used to pay for the service.