Just got a galaxy watch 46mm and couldn't get Samsung pay to work, was informed that the watch is from the Baltic region and Samsung pay doesn't work with them
you can't blame samsung. it's the ebay sellers fault. they will of bought them cheap from Europe avoiding paying UK tax on them and resold them to you. your best bet, if you payed by PayPal contact them and tell them the item is not as described. ie: not suitable for the UK market. ebay is flooded with galaxy watches mainly the active model and regularly sell for £80/£90.
I bought my first Samsung watch off a seller on Amazon and that was from Europe and Samsung pay didn't work on that the seller didn't want to know nether did Samsung and the just disappeared from Amazon so what I think is that they buy a job lot sell them and then disappear