Thanks for using Apple Support Communities. From your post, it sounds like you're having playback issues when using the Sky Go app on your iPhone 7. It sounds like you've tested a few components and made sure your device was updated as well. The article below offers additional info to get you pointed in the right direction.
About Apple Digital AV Adapters for iPhone, iPad, and iPod touch
If you still need help.
Find out what to do when you have the following issues.
Make sure that you're using a Digital AV adapter (which has an HDMI port). If you're using a VGA adapter, it doesn't carry audio signals. To hear audio with a VGA adapter, you need to connect to the headset jack on your TV, monitor, projector, or stereo.
The app might not be compatible with your adapter. Check compatibility on the app's info page in the App Store or contact the developer.
Your content might not be compatible with your adapter. Movies, TV shows, and certain streaming video apps require High-Bandwidth Digital Content Protection (HDCP). If you try to play these movies, shows, and streaming videos using a non-HDCP digital connection—like the Apple VGA Adapter—an alert will ask for an HDCP-compatible device.
- Disconnect and reconnect your adapter from your iPhone, iPad, or iPod touch and from your TV, monitor, or projector.
- Make sure that your VGA or HDMI cable works, since the issue could be with the cable.
- Remove any VGA or HDMI extension cables or converters. Accessories that convert a VGA or HDMI signals to different video formats (DVI, Composite, Component) aren't compatible.
- Make sure that you have the latest version of iOS.
For more help, contact Apple Support, to set up service for your: