Who Should Use IOSS?
Any UK business selling goods to EU consumers with values under €150 (£135) should consider using IOSS. Unless you only sell on participating marketplaces (eBay / Amazon / etc.)
If your business only sells on participating marketplaces (eBay / Amazon / etc.), it is the responsibility of that marketplace to collect applicable EU VAT charges on goods and pay them to the relevant EU Tax authority via the IOSS system.
In this scenario, you will be given an IOSS number by the marketplace to enter when booking your parcel.