The existing Office 365 service is currently in Neural Portal
Select this option if the customers' existing Office 365 service is provided by you and the service is already in the Portal. You'll be asked to select the existing service. Any migrations or licenses ordered will be directed to the existing Office 365 service.
The customer already has an Office 365 service with a 3rd party provider
Select this option if the customer already has Office 365 from another provider. In order to move a customer from an existing provider, you may be able to do a license transfer, or it may require a standard migration.
If you're unsure whether the current service is with Office 365, please see the following article: Office 365 New or Existing