The following troubleshooting steps can be taken in order to investigate why your smart TV is not responding to voice commands for specific apps:

1. Check whether the microphone of your Smart TV is turned on and is working correctly.
2. Check if the voice command recognition for the app is enabled.
3. Check if the app is compatible with voice commands offered by your Smart TV’s voice recognition engine.
4. If you are using external devices connected to your Smart TV, make sure they are properly configured and connected.