We had someone else from Sweden saying the same thing a few days ago so it seems it's definitely a problem with ebay.
Ask the seller to put your ID on their exemption list which will lift any blocks. They'll find it on their My eBay at Site Map at the very bottom of the page. Scroll down past the categories to Sell > Selling Activities > Manage Bidders.
Or send them this link:
https://www.ebay.co.uk/bmgt/ExemptBuyers