IEN number is one of the core measures taken by Amazon UK to combat the abuse of VAT rules by cross-border e-commerce sellers outside the EU. It will be implemented from April 1, 2018. If you cannot provide IEN number, you can try the following methods:

1. Update the IEN information of the shipment in your seller backend and confirm that your shipment "cannot provide IEN".

2. If you have provided the UK VAT registration number and used it for customs clearance, you can save your "IEN" entry in the UK customs clearance form, and the status will be displayed as completed.

3. Please note that Amazon has a transition period of 240 days for sellers. Even if you update the IEN information (fill in IEN or confirm that IEN cannot be provided), you can still sell normally.