Marketplaces bunch Northern Ireland in with the rest of the United Kingdom for VAT purposes and just do the easiest method for them. E.g. Amazon doesn't put XI VAT numbers on invoices to EU customers, just uses BT postcodes. And eBay treats NI to EU sales as domestic transactions even if the seller is registered for OSS in Northern Ireland.

In all cases however we do not use IOSS and this may cause confusion when the destination customs officials scan the electronic customs data and see the marketplace IOSS number.