A: Yes, when Modul att synka (under Försäljning in the Fortnox app settings) is set to Faktura. This works in both Fortnox and Fortnox Premium. In Fortnox Premium, Order & Faktura also syncs credit invoices.
A credit invoice becomes a sale of its own in Upsales, with a negative value. It is not linked to the sale of the invoice it credits.
With Order or Order & Offert, invoices from Fortnox, credit invoices included, are not created as sales in Upsales.
In Fortnox Premium, credit invoices do not sync while Inaktivera synk från Fortnox is ticked.