The Office 365 portal does not allow you to revoke an individual license if it has a dependency on other licenses. For example, an individual license is dynamically allocated to a resource in the User Application.
To workaround this issue, remove the dependent licenses before attempting to revoke the individual license. For example, if Office Online for Developer license is dependent on SharePoint Online for Developer license, you need to revoke Office Online for Developer license before you revoke SharePoint Online for Developer license.