Do you have a Premium Spotify account? Before you start this, please note that only Premium Spotify accounts can be linked to Amazon Echo.
To link your Spotify account to an Amazon Echo, first open http://alexa.amazon.com and then click on Music & Books. Then, click on Spotify under the Music section.
When prompted, click on “Link your account”
Click Log In To Spotify (unless you don’t have an account, then click “Sign up for Spotify” to setup an account)
I use my Facebook account for Spotify, so I’ll click “Log in with Facebook”
Then, grant access when prompted.
Now, you can say “Alexa, play Halloween mix on Spotify” and you’ll hear this (or I will):