New Validation Rules for E-Invoicing

Which rules will apply?

• Mandatory reference: The Your reference / Your electronic reference field must be populated when sending an e-invoice.

• Positive unit price: Line items can no longer feature negative unit prices. Negative quantities and negative line totals remain valid, but the unit price itself must be positive.

• Customer verification: To send e-invoices, the customer must be customer-verified or connected to an agency.

What does this mean for your integration?

Validation occurs prior to dispatch. If an invoice is sent from an unverified account, the API will return an error response. Please ensure your integration handles this error appropriately and helps guide users to complete their verification in Fortnox.

When do these changes take effect?

Since these changes impact live integrations and user workflows, we're providing advance notice so you can update your codebase.

The new validations go live on October 19, 2026. Please ensure your integration is updated prior to this date.