To address this problem, login to deploy.apple.com and accept the new terms and conditions. All DEP administrators must accept the new terms to continue managing MDM servers and devices.
However, only the Agent can reactivate the service for an organization. The Agent is the Apple ID that originally setup the DEP account with Apple. Only the Agent will have an Admins tab after logging in. Once the Agent accepts the terms and conditions, DEP access will be restored and everything should behave normally.
Unfortunately, at this time there is no tool to determine who the Agent for an organization is. If this user is unknown or cannot be found, please contact Apple support.
For more information, please refer to the following Apple support article.