New fields on Customer Invoice: `purchase_order_reference` and `sales_order

Two new optional fields are now available on customer invoices to support e-invoicing requirements (EN 16931 standard).

New fields

Field	Type	Max length	Description
`purchase_order_reference`	string \| null	50	Buyer's purchase order reference (BT-13)
`sales_order_reference`	string \| null	50	Seller's sales order reference (BT-14)

Both fields are returned in all customer invoice responses (create, import, show, update, finalize, etc.) and default to null when not set.

Where you can set them

The fields are accepted on the create and import endpoints:

POST /customer_invoices — draft and finalized creation
POST /customer_invoices/import

{
  "purchase_order_reference": "PO-2026-001",
  "sales_order_reference": "SO-2026-001",
  ...
}

Validation

Both fields must be 50 characters or fewer. Requests exceeding this limit are rejected with a 400 Bad Request.

Scope required

These fields are included automatically in existing responses — no scope change needed. Writing them requires the existing customer_invoices:all scope.