I see picture but no sound
Sound out of the iPhone, picture on the TV — fix the audio routing.
This is the #1 setup issue and it's almost always one of two causes:
1. Silent mode is on
The orange/red switch on the side of the iPhone silences app audio over AirPlay too. Flip it back. iOS Settings → Sounds & Haptics confirms the state.
2. Output is still set to iPhone
iOS Control Center → tap the music tile → tap the AirPlay icon → pick the TV.
For DRM-protected streaming apps, audio is sometimes intentionally muted on external displays — that's a rights-holder restriction, not Air Cast.