"So i figured out the issue, there must be a unicode issue with the launcher, as my steam username was in katakana, once i changed it to english it let me link, so if you have any non english characters, id suggest removing them from your steam name, once youve done the initial linking you can change it back"

I can confirm, i changed my steam username to a simple name (was using cyrillic) and it lets me link it!
Hope it helps!