A TV that is off is no longer reachable on the network. For the app to turn it back on, enable Wi-Fi wake-up on the LG TV.
Enable wake-up on the TV
- On the TV: Settings → General → Devices → Connection Manager → Mobile TV On (the name may vary by model).
- Turn on « Turn on via Wi-Fi » — and « Turn on via Ethernet » if the TV is wired.
- Connect the app to the TV while it is on at least once: it stores the hardware address needed for wake-up.
Usage
After that, the app's power button turns the TV back on even when it is off. Wake-up only works if the phone and the TV stay on the same network.