I have the same issue. Works fine on my S8. No app available in the wearable app same as your screenshot. Brand new galaxy watch (SM-R800) bought from reputable UK seller today 27/12718.
Cannot find any answer on web. Samsung moderators please progress these issues.
My problem with Samsung Pay solved. Although the Galaxy Watch was purchased in the UK, this turned out to be a Romanian version. Should have realised when the default set up language was Romanian!! Returned to dealer and explained and offered a full refund. Went to another retailer and bought UK version, model number ending in ABTU. Works perfect straight out of box. No Samsung Pay issues :-)
This is good news congrats. I have spoken with my partner who got me the watch and she purchased it from Appliances Direct, and the wording shows Samsung Pay should work etc.
Samsung Galaxy Watch 2018 Bluetooth 46mm - Silver
I have emailed them with my issue and asked for confirmation the watch they supply is 100% a UK model.
Will update when they come back to me in 48 hours
That's where I bought my first one. There should be a sticker on the box. Mine said SM-R800NZSAROM and as I posted earlier, when setting up the default language was Romanian. Also, the advert on the website says it is SM-R800NZSABTU. But mine obviously was not. Offered me refund, apparently no alternative I.e. UK version could be offered.