I have a Chromecast 1 with latest firmware. I signed up for Spotify premium today and installed the app on my Iphone. So everything is up to date. My Chromecast works fine with other apps. It is on V1.17.46278. I rebooted them to be sure.

When I play Spotify on the phone, I have a bar at the bottom that shows the track playing and it shows the Chromecast logo and says 'devices available'.

However when I press that bar and the music shows now playing with an album cover picture there is no option to cast. I simply dont see the device or any options. 

Pandora casts perfectly from the same Iphone.

Thank you for any help

Brian