A: Set Modul att synka (under Försäljning in the Fortnox app settings) to Order or Order & Offert. Invoices from Fortnox are then not created as sales in Upsales. Faktura syncs invoices, and so does Order & Faktura in Fortnox Premium.
When a Fortnox order that is linked to a sale in Upsales is invoiced, the sale still gets the invoice number, whether the invoice is paid, and its number of reminders.
In Fortnox Premium, ticking Inaktivera synk från Fortnox stops the ongoing sync from Fortnox to Upsales. A full import that you start yourself still runs.