None of the above solutions worked for me. UNlinked and re-linked through a variety of browsers tens of times. Did a lot of research online and the fix on this reddit post from Jay7962 was the only thing that worked: https://www.reddit.com/r/amazonecho/comments/5h9ptf/echo_dot_not_playing_spotify/
Basically, the problem seems to be with Spotify. Say 'Alexa Spotify Connect' and then she will tell you to choose the Echo Dot using Spotify Connect within the Spotify app. I then logged in on the desktop version and did exactly that. All working now!
hi had same problem you need to go to amazon -> your account --> digital content --> manage content and devices--> then youll see settings and you need to change the country to us