If you require events/opportunities to be approved before they are published, you can turn on the 'Approval' workflow within your Account.
Turning on the Approval System
A new account setting called “Events require approval to publish“ will require events to be submitted for approval before they are able to be published to the portal.
- Only specific admin roles will be able to ‘approve and publish’ an event, which is controlled by a new admin permission ‘Event > Approve’
Submitting Events for Approval
Administrators without approval permission will be able to create an event and save it as a draft (unpublished) or Submit for approval.
Approving Events
Administrators with approval permissions can filter events by Approval Status to determine which events need to be reviewed. 
When updating an event, administrators can Save & Reject or Save & Approve.
When rejecting an event, administrators will have an opportunity to leave comments
