When IOSS Fails at Customs: What Sellers & Customers Need to Know

Selling goods into the EU under the IOSS (Import One-Stop Shop) scheme usually simplifies VAT handling at customs. But occasionally, parcels with correctly prepaid VAT still get caught in customs systems — either held or charged again.

That’s exactly what one of our clients recently experienced, and we want to make sure you (and your customers) are prepared — and have a clear playbook to resolve the issue.

1. Proactively inform customers: “VAT already prepaid via IOSS”

One of the easiest and most effective preventative steps is clear communication. Before you ship:

• Ask your logistics or fulfilment team to include a message in the dispatch or shipping confirmation emails, such as:

“VAT for your order has already been prepaid under IOSS. If you receive a customs or VAT charge request, please contact us before making any payment.”

• Encourage customers to let you know immediately if they receive a customs charge request — this gives you a chance to intervene before they pay.

• Doing this builds trust, reduces confusion, and gives you early visibility into validation failures.

2. Don’t share your IOSS number directly with customers

You might think handing over your IOSS number to the customer would help, but in practice, this isn’t advisable. Risks include:

• Potential misuse or fraudulent declarations

• Confusion if customers try to use the number improperly

• It does not guarantee resolution: customs systems may still reject the number

Instead: share your IOSS number only with fulfilment providers, postal or courier partners, or customs authorities when necessary — you remain in control of how and when it’s used.

3. If the goods have already cleared customs but VAT was charged: customers must claim a refund

Sometimes, despite a valid IOSS registration, customs accepts the parcel and releases it — but still issues a VAT charge to the recipient. In that case:

• You cannot retroactively apply the IOSS number to that clearance.

• The recipient needs to request a refund from the postal or courier service that collected the VAT.

In their request, the customer should explain:

• That VAT should have been paid under the IOSS scheme

• The shipment was not sent under DDU (Delivery Duty Unpaid) terms

• That the VAT/customs charge was made in error

For instance, in countries like the Netherlands, customers can request the postal/courier to invalidate the import declaration if VAT was unnecessarily charged. PostNL allows submitting formal objections or refund claims (typically within a specific timeframe after clearance).

Because PostNL sometimes sends follow-up communications directly to the recipient, it’s more efficient and timely if the customer handles this process themselves rather than you doing it for them.

When reimbursing the customer, ask for proof of payment and any relevant customs or postal invoices — that helps you reconcile internally.

4. Why Postal services may contact customers directly

In some cases, when a VAT or customs charge comes through, postal services may send requests or emails directly to the recipient. Because of that:

• It’s more practical for the customer themselves to handle the refund or objection (rather than relying on you chasing on their behalf)

Your support team should be ready to guide customers:

• What forms to use

• Which documentation is needed

• How to frame their request (i.e. explaining that VAT should have been prepaid via IOSS)

• The typical objection windows or deadlines in that country

This approach prevents delays, miscommunication or missed deadlines stemming from third-party “passing along” of requests.

5. If goods are still held by customs: retry with IOSS

If your parcel is stuck in customs and hasn’t been released, there’s still hope:

• Ask the fulfilment centre, postal or courier provider to resubmit or amend the customs declaration (e.g. CN22, H7 forms) including your IOSS number

• In many cases, customs systems may accept the IOSS number on retry

If resubmission fails and the IOSS number still can’t be verified: escalate. Contact Lumiopro and we can intervene. We will liaise with the local customs office or the EU IOSS registration authority and provide a copy of your IOSS certificate to support the reclassification or release of the goods

This is often the most direct path to freeing stuck parcels without forcing unnecessary costs on your customer.

6. Suggested internal workflow (for your team)

Here’s a sample workflow your operations, support and logistics teams can adopt:

Situation	Action	Key Notes / Tips
Customer receives a customs / VAT charge notice	Ask them not to pay immediately, and notify you	The charge may be erroneous
Goods already released, recipient paid VAT	Guide customer to submit a refund / objection to the postal/courier	E.g. PostNL objection or other local processes
Goods held by customs	Ask fulfilment or courier to retry with IOSS on customs forms	Use CN22, H7 or equivalent
Resubmission fails	Escalate to Lumiopro / IOSS intermediary	Provide certificate, liaise with customs

You can embed this workflow in your internal documentation or use it as a playbook when IOSS issues arise.

7. Sample message you could send to affected customers

Hello [Customer Name],

We’re sorry that you’ve been asked to pay VAT or customs fees on your delivery even though VAT was prepaid via our IOSS registration.

Please do not pay this request immediately — contact us first so we can work with the postal/courier to retry the IOSS declaration.

If your parcel has already been cleared and you’ve paid VAT, we’ll guide you through claiming a refund or filing an objection with the postal/courier.

Please send us your proof of payment, any customs or postal notices you received, and your parcel tracking info. We’re here to help you through the process.

You can adapt this message for emails or chat support templates.

8. Best practices & key takeaways

• IOSS validation issues are often glitches in customs’ systems — not problems with your registration

• Proactive transparency with customers reduces confusion, disputes, refunds, and support overhead

• Keep internal teams aligned: logistics, fulfilment, customer support all need to know the process

• Document your IOSS credentials, receipts, and any customs correspondence — you may need them for escalation or proof

• When things go wrong, stay calm, follow the steps above, and lean on your intermediary (Lumiopro) to help with customs or authority escalation