Use Google Assistant SDK to initiate Spotify playlist streaming to Chromecast device

I’m trying to create a script to make use of the Google Assistant SDK, to initiate streaming of a Spotify playlist to a specific Chromecast device. I’m using a script because I have a few other devices involved in the process, ie Amp).

I have Spotify as my default music app and have a premium subscription linked within Google Assistant.
I have tested the command simply using Google Assistant and it plays fine, however using the SDK, gives the response that “Sorry, I cant do that yet”.

Is this possible or is this in fact a current limitation of the integration.

Thanks