CustomerID
I need a Customer ID (not an Organization ID) how do I obtain one?
MacBook
Find Apple Customer Numbers, Reseller IDs, and Organization IDs...
If you purchased from Apple
When you purchase from Apple, we assign an Apple Customer Number to your organization. If you don’t know your Apple Customer Number, contact your finance department or Apple Sales.
If you buy Apple devices from an Apple Store, ask the Business Team for your Apple Customer Number.
If you purchased from an Apple Authorized Reseller or wireless carrier
Contact your Apple Authorized Reseller or wireless carrier.
Confirm that they support the Device Enrollment feature of Apple Business Manager or Apple School Manager.
Ask for their Reseller ID.
If they don't support these programs, ask them to contact their distributor or Apple account team. If they choose to participate, they'll work with their distributor or Apple to start supporting Device Enrollment.
https://support.apple.com/en-us/HT204401