Registration and intermediaries

Before anything else

The plugin needs an IOSS number to be useful, and getting one is the step most stores underestimate. IOSS registration is voluntary — but without it, your EU customers pay import VAT at the border plus a carrier handling fee, and refusal rates climb. This page summarizes who registers where. It is a practical overview, not legal advice; confirm your own position with a tax professional or intermediary.

Who registers where

  • EU-established businesses register for IOSS in the member state where they are established. (If you are EU-established and dispatch from inside the EU, you are in OSS territory, not IOSS — but an EU business dispatching from a non-EU warehouse is in IOSS scope.)
  • Non-EU businesses cannot, in general, register directly. You must appoint an EU-established intermediary, and your member state of identification becomes the intermediary’s member state.
  • Norway-established businesses are the one exception: Norway has a VAT mutual-assistance agreement with the EU (the only country listed in Implementing Decision 2021/942), so a Norwegian seller can register directly — but only for goods dispatched from Norway. A Norwegian seller shipping from China still needs an intermediary.

The intermediary requirement

An intermediary is an EU-established business (typically a tax firm or a specialized IOSS service) that registers on your behalf, files your monthly returns, and is jointly liable for the VAT. Intermediaries charge for this — usually a monthly fee — which is a real cost of the scheme for non-EU sellers, and there is no way around it apart from the Norway exception. The intermediary receives its own IN-format identification number and a separate IM number for each seller it represents; the IM number is the one you enter in the plugin.

GB sellers

Great Britain is treated as a non-EU country for IOSS: despite the UK–EU trade agreement, the UK is not on the mutual-assistance list, so GB-established sellers need an EU intermediary like any other non-EU seller. Two UK-specific points:

  • HMRC opened intermediary registrations on 1 April 2026 on its own IOSS service, so UK-based intermediaries can now register and represent sellers through HMRC.
  • Northern Ireland is in the EU goods VAT area under the Windsor Framework. NI-established businesses can register for IOSS directly through HMRC, and rest-of-world goods shipped to NI consumers in consignments up to £135 can fall under IOSS. Note that GB→NI sales are not IOSS — they go on the normal UK VAT return. The plugin treats Northern Ireland addresses (country GB, BT postcodes) as the EU destination XI automatically.

The IM number format

An IOSS number is 12 characters: IM, a 3-digit numeric country code for your member state of identification, a 6-digit number, and a check digit — for example IM276000123X shape-wise (not a real number).

The plugin validates the format only. There is deliberately no validity lookup: unlike VAT numbers and VIES, no public registry lets anyone confirm an IOSS number is live — only member-state customs authorities can query it. A format-valid number that has lapsed or was mistyped within the pattern will pass the plugin’s check, so copy it carefully from your registration confirmation or your intermediary.

Entering it in the plugin

Enter the number in the setup wizard or later under WooCommerce → IOSS → Settings. It is stored on each captured order and — with Pro’s customs data layer — passed to shipping integrations, which is where it actually earns its keep: a missing number at customs means your customer pays VAT a second time at the border. See Customs data.