Have Now TV and a number of other apps on an iPad. All of them cast OK to a TV that has a plug in Chromecast device.
All of them except Now TV cast OK to a Sony AF9 with a built in Chromecast. When I try TV switches to Chromecast and shows a Now TV background but then never gets past the spinning colour dots before TV and app drop back to previous screens.
Don't know if a NowTV or Chromecast issue. I have reinstalled app and am within device limits on Now TV.