BREXIT / IOSS / VAT

[mbealing]

Im in the UK, customer in Belgium just refused a delivery from me (t-shirts) as the Postman attempted to charge him 42 Euros. Presumably import tax or VAT . this is a fist for me, as nothing like this has happened in 10 years of selling to Europe. Must be a Brexit thing, I think. So I go back and look at the messages from eBay urging me to become compliant before July 1, and get an IOSS number : 

"Share IOSS number for EU imports: where eBay has collected VAT on your shipment from the UK to the EU (up to a consignment value of 150€), always electronically provide to your carrier the Import One-Stop Shop (IOSS) number provided by eBay. Otherwise, your buyers may have to pay VAT again on delivery."

Well I have clicked link after link and can see nowehre to get the number from , or how to share it or to whom.  Anybidy as thick as me and have the same problem?