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New `contract_reference` field on customer invoices

October 22nd, 2026 by Integrations Squad

You can now set the contract reference of a customer invoice through the API. It corresponds to the e-invoicing field BT-12 and is included in the Factur-X of the invoice.

What's new

  • contract_reference can be sent when creating a customer invoice:
    • POST /api/external/v2/customer_invoices (draft and finalized invoices)
    • POST /api/external/v2/customer_invoices/import
  • contract_reference is returned in all customer invoice responses.

The field is optional and nullable, with a maximum of 50 characters.

Example

{
  "contract_reference": "CT-2026-001"
}

This is a non-breaking change. The new field is additional and does not affect the existing response structures.