ProvisionInput

The customer, matched by externalId (case-insensitively) and created if new. On a match, name is replaced and the other fields only when you send them.

Where the deal comes from.

A contact at the customer, matched by externalId and created if new; on a match every field is replaced by what you send. Answers 409 CONTACT_CUSTOMER_IMMUTABLE when the externalId is another customer's contact. It becomes the order's billing contact unless order.billingContactExternalIds names others. Afterwards it is an ordinary contact: read or change it with Get a contact by external ID and Update a contact by external ID.