MMS - Login to Spotify with Your Facebook login

In order to login with a Spotify account created via Facebook, one must create a username and password for devices. If you login to Spotify.com, select 'Edit Your Profile', and then Set Up A Username for Devices, you should be able to use that username and password combo on the MMS.

Spotify.com->Edit Your Profile->Set Up Username for Devices

In the US, the direct link to this page is: https://www.spotify.com/us/account/set-device-password/