Problems using Chromecast with Spotify on iPhone

[Supermand]

I have problems using Chromecast with Spotify on my iPhone 6 as Chromecast doesn't appear on the list of available devices. Chromecast works fine with other apps so I suspect it must be a problem with Spotify. I have the latest version of Spotify (version 5.7.0), the latest iOS version (9.3.4), 2nd generation Chromecast device and I have a premium Spotify subscription. I have tried disconnecting Chromecast, deleting the Spotify app, disconnecting the TV, rebooting my internet connection and nothing works.

Does anyone know how to solve this?
Thanks!

[catootje]

Exactly the same here. Also iphone 6 with latest iOS 10.0.2 update.